Personally I would probably run Mitsubishi Evo running gear if you want lots of power. The front cossie diff and the cossie gearbox is not very strong for anything over 400 ftlb of torque...the uprated stuff is quite pricey. My diffs and box ran over £10k to handle 469bhp and 500 ftlb.

I have got a 205 gti6, I imagine a turbo would corrupt the chassis even with lsd.

What body kit will you run to cover the 4x4 width? Maxi, t16, Dimma or just wide arch spats