I've worked on both the KWA and CA. Quite a few clients owned them and I personally owned both at one point as well.
Both guns have their ups and downs really. But if you have perfect confidence in gearbox upgrading, go with CA. It's a much better base and 100% compatible to just about anything M4 out there. But you start out with a not-so-great performing gun(IN MY STANDARDS). 330FPS gives you mediocre range, accuracy is meh(Hop up rubber is below par), ROF is meh, though the externals are great.
However if you don't want to touch anything and just want to play it stock, the KWA will outperform a CA anyday, Range, Accuracy, ROF, Mechbox durability, you name it. The only thing I hate about KWA is that you can only use 2-Piece hop up units unless you do major reconstructive surgery. And some other parts are not TM compatible as well.
Both guns can perform superb if you tune it up properly with the proper parts(I can say the same to just about any guns out there on the market).
Hope that helps
Last edited by Skladfin; May 11th, 2009 at 02:15..