RCM had a test article on the Kyosho pitts a while back, they liked it with the OS 46FX, (best engine for the buck these days) and a Slimline Pitts muffler.

Also every 40 sized bipe I have heard of is supposed to fly better with mini servos in the wings, with HS81s or 81MGs you can lay them sideways in the wing and just stick the servo horn out instead of hogging the whole regular sized servo into the wing and letting it stick halfway out the bottom.

The master builder over at Venture Hobbies (my LHS) just built a gorgeous one and can probably give you a hint or two. Ask for Larry, (847-537-8669). He has some nice pics too.