It's a combination of things.
Mostly it's the fact that a Speed is a very high aspect ratio kite that is also very flat.
It has the most power when flown lower. When flying a kite lower you need to have a board that is very efficient at edging... like a knife slicing through water. For this a really thing low rocker twin tip is best.

On the other hand a surfboard has a nice round fat rail and good rocker. This will be less efficient at edging.

With a surfboard it is more about riding light and with your weight far forward on the board. Board flat and taking advantage of lift from the kite. A kite that is faster turning will also help more on a surfboard as you can work it harder using the lift at the top of the signing motion.

Things also change when you throw a foil board or a race board. The much larger fin effect works like a twin tip edging.

Also a low rocker gun type surfboard with some concaves will work way better than other surfboards with a speed.

I have years of experience on the three Speeds.

Thanks for the reply Fred. What types of twin tips would have low rocker, or does it change from board to board? My current understanding is that Wakestyle boards generally have lots of rocker, so my first guess for a low rocker board would probably be a high performance Freeride/Freestyle board. What about the Underground Crypt? (Looks like a awesome board and I have heard it has low rocker) I am not currently in the market for a new board right now but was just wondering for future reference.
Thanks!!
-Cullen

Flyboards work well with the Flysurfer - I like the Flyradical3 and I hear the 4 is better!

The 12 is for sure the right choice for you at your size but the speed 3.5 has such a big range that I have even had my wife at 100lbs. ride my 21m at Litewind demos!!!! But she can ride the 12m speed 3.5 on a small board as soon as I can ride the 21m on a med to large board, I am 200lbs.
Please hit me up if you have any direct questions... Later ted B

I'm not familiar with current twin tip models, but the Flysurfer boards are well suited to the Speeds.

Yep...and the Spleene Doors have always worked pretty well with the Flysurfer kites. I use a 154cm Door with my 15m S3 in lower winds and switch down to a Super Shinn 135cm in the mid teens.

If you've the chance some experimenting with what you like to do is best. I know, for instance, that some people have had good results with the Ocean Rodea Mako series but I've no experience with them.

You really have to try the Shinn boards; they plane very fast and they are chop eater. Great TT.

I am now waiting for the Shinn King George; in the meantime I use an Epic Oxygen and I have to say that it also performs really great. It really is a good combo with my Speed 3 19 or 12. Rest of the time I use a Supershinn 135 wich gets me going in the mid teen also at 170 pounds