I use a 3.5, seems to cope with everything I've thrown at it yet!!
The gap between it and my 5.5 bee seems just right.
Great, Great Kite, easy to fly, surprising amount of pull. I can buggy with it in moderate winds without even trying to work it ... just hang it like a sail.
My one complaint about bullets still stands though...land it at the edge of the window, tends to 'fold over' when it's on the ground and needs a visit to fix it... this happens for me easily 50% of the times I land/crash it at the very edge of the window ... pain in the backside to have to get out of the buggy...my bee seems to be able to be 'shaken' out of most situations like this, but the bullet won't budge ......but .......well worth the bother for all that!!