To the original poster: in short, choose whichever kite you prefer, but do not be too quick to discount 5-line kites based on a few forum responses:
This issue will never die and I'm sure that I've written this same message before, but there are advantages and disadvantages to both 4- and 5- line setups.
There are also a lot of myths and exaggerations. It is true that North has the patent on 5-line kites. Our best selling kite, the best selling kite of all times, the Rebel, is a 5-line kite. As North is now the best selling brand in the world, it's the easiest way for other brand reps/salesmen/pimps to take a swipe at North, by telling people that 5th line wraps are awful, will involve cutting your kite in half, and will at the very least require a swim in.
When you wrap the 5th line, it does not slice the kite in half. It will slide off to the side, and just like a 4-line kite, you can relaunch like normal, ride like normal, and go back to shore to relay your lines (which you'll need to do with a 4-line kite as well). I have heard enough people swear on this forum that they've been involved in a 5th-line wrap that somehow required them to swim, so I assume that this may be possible, but I've been riding 5-line kites for 10 years now and have NEVER had that happen. I even broke a leash a couple years ago, watched my 5-line Vegas tumble through itself for 5 minutes while I tried to flag someone down, finally got a ride (thanks again, Britney), got to my kite with the 5th line wrapped around it several times, brushed the wrapped lines off the bar, hooked in, watched the 5th line slide off, relaunched the kite like normal, and rode back upwind with a cat's cradle of a line set to where I'd originally snapped the leash, dropped the kite to the 5th, relaid the lines, relaunched, and kept riding.
Again, I have no doubt that it is somehow possible to wrap your 5th line in such a way that it is impossible to relaunch and will require a swim, but I've never personally done or seen it.
As to 5-line kites in the waves... I have no doubt that it is possible that a wrapped 5th line in conjunction with the kite getting smashed by a big wave can cause the kite to rip in half, but any kite that gets smashed by a big wave is probably going to get torn in half. Personally, I prefer 5-line kites in the waves and I think it helps keep the kite safe... I can use the 5th line to relaunch the kite more quickly, and if there's no chance of getting it up and I can see a wave heading at it, I can release to the 5th line, so the kite lays on its back with far less chance of damage than a 4-line kite taking it squarely.
As far as 5-line kites only being useful for 'mowing the lawn', I learned unhooked kiteloops and F-16s on a 5-line Vegas back before we had the suicide ring, so I was dropping the kite to the 5th literally dozens of times a session without problem. Many of the most advanced riders in the world are riding 5-line kites like the Torch and the Vegas.
For safety... North has a 2-line front line safety system that I consider to be among the safest 4-line systems on the market. But I do not consider it to be as safe as a 5th line. 95% of the time the 4-line system will work just as well, but it will often need to fly through the window and have you move a small distance towards the kite before it flips over onto its nose like a 5th line, whereas with the 5th line the depower is instantaneous and complete every time. If you're standing just upwind of rocks or sketchiness while launching or landing (as I often am in the Gorge), this small difference can save your life. Plus, if you're doing self-rescues in 30-40 mph winds, then the advantage of the 5th line safety really shines. Another quick story... I was at a spot in the Gorge where you launch and land on a smaller sandbar. It's pretty easy to self launch and land in reasonable wind, and it was at the upper end of reasonable when I got there. I was on a 7m, as were some others. It soon picked up significantly, and I was headed back to the sandbar where I saw two people on 4-line kites with a single frontline release. They were trying to land each other with their kites in the air, but in the insane wind they couldn't pull it off. when I got to the sandbar they were kind of freaking out. I told them to release the kites, but they said that though the safety worked in reasonable winds, the kites could start death spiraling in high winds. I had no qualms with popping my 5-line safety (the kite floated upside down about 2' off the water, don't think it even touched the water on the way down), sanded down my twintip, clipped my leash to the board and easily landed their kites while my kite sat calmly just off the water with nothing more than a twintip and a couple handfuls of sand holding it in place. If I'd been on any 4-line kite I would not have been comfortable doing any of that.
Finally, there's the added risk of bridle issues that you will not get with a 5th line kite. The closest I've come to dying while kiting was with some guys up in Montreal, self launching a 4-line kite. I attached everything correctly, but while self-launching, one of the bridles got tangled or wrapped and the kite started looping, with me about 50' upwind of a cement wall. Luckily I hit my release and the safety worked correctly, but it was pretty scary and required quick reflexes and would never have happened on a 5-line non-bridled kite. And the guys I was kiting with at the time tell me that there are still kites out there with a long enough bridle so that they can tangle in such a way that even if you hit the release, the kite will continue to death-loop.
For all of these reasons and more, I personally, and North as a brand, firmly believe in the viabillity and usefulness of 5-line kites. At the same time, I don't try to change anyone's mind who has had a problem with 5-lines, and I certainly am not saying that you can't have problems with the 5th line. North has more 4-line models than 5-line models. I ride both styles on a regular basis. In my opinion, most of the time you don't notice a difference. I don't blame some people who have had issues with 5 lines for choosing to use a 4-line setup, but for me personally, all else being equal, I prefer riding 5-line kites, and if you prefer the way one kite rides to another, I wouldn't let the number of lines be a deciding factor.
And this long diatribe doesn't even address the performance differences between the setups (there are significant differences in "feel" and performance of 5-line vs 4-line) but that's something you should find out first-hand by demoing.