Hi Ice,
When it comnes to the P40, GSP is MILES ahead of WM.
I had the WM version and really was not that impressed.
Weak mechanical retracts (I eventually junked them for Hobbico units) and although the balsa and fibreglass build quality was really good, as was the painted finish, frankly, I have flown better handling models.
I sold my WM P40 on and looked at both the (in my opinion, overpriced,) Kyosho version and the GSP one.
The GSP example is now in my possesion.
Only trouble is that it is finished in a silver color scheme.
I will paint the model up in either WW2 RAF Desert scheme in the markings of 112 Squadron RAF, who also used the "Shark Mouth" on the cowl, or 76th FS, 23 FG USAAF (the descendents of the AVG.)
Both versions used a similar tan & brown camouflage scheme with light blue underside and red spinner.
Paint? Probably just an enamel, like Humbrol, or maybe Lustrekote if they make the correct brown to go over the tan. Lustrekote does come in Olive Drab if you want to do one from a different WW2 theatre.
I won't bother with retracts on this one. I fly off grass and found from my last P40 that they were nothing but trouble.
If you want to fit them, (the kit is designed to have them fitted) try a good quality brand like Century Jet.
Don't waste your money on el cheapo's. It's not worth it.
Power will either be an ST GT51 2S or a Saito 65 4S. Both will be fine.