I mod / rebuild my bars but your questions are pretty specific. I would try to cast a wider net. Few people do this and I bet fewer do 5 lines and even fewer are specific to wake style.
I'd love to know from where you come from with these figures.
Just few examples: all the fuel riders who fly with a 5th line mod their bars, Hadlow itself modified the north bar to use his 6th lines mode. Some Ozone C4 riders get rid of the bridles to set a 5th lines bar.
Back on topic.
line lenght: with my actual set 7-9-11 I'm using 22-24 mt long lines. When I had the 5 I used 20mt long lines.
What I want on my bar is
1) thin diameter bar (flexifoil one is thin)
2) low V. So if I tangle I can untangle without come back on shore.
3) Oh Shit rings. Maybe you're never going to use them but in case of strong wind when you know that even relasing with the 5th the kite is still going to fly, well you'll appreciate have them.
4) good lines. I like Ozone, Slingshot and I never had problem with Airush or Flexifoil one.
5) Large CL with PU coated depower line. I've a 2014 Ozone one
6) above the bar depower trim. It's easy to replace and I find it more precise than the pull pull one.
About 5th line modification, on my Hadlow pro which had the same problem you have with the GP I did this:
I added a 3mt long 3mm diameter line from the V with a spliced hole in both the end. On the hole far away from the V I let pass my 5th line with a metallic ring larger than the hole so it is fixed with the V and my 5th doesn't slack when I depower.
Then you need another line from the ring to the CL for the safety.
I hope this is clear enough otherwise I can post some pics. But I can take really long time