In any differential design there will be lost HP and the biggest job they have is staying in one piece and making both wheels transfer power instead of just one (in the case of a limited slip diff or spool) and doing it quietly. You can make stronger and more efficent differentials but they are noisy as hell and I'll take the extra few HP lost for a quieter gear profile.
The SVX diffs looked pretty damned beefy the last time I was under SVXtasy's car, the problem with the drivetrain is going to be making a transmission * center diff stay in one piece, as hard launches in heavy AWD cars kill trannies like no other. Adding sticky tires like drag radials or slicks only make it worse.

The Garrett GT designs are excellent turbos, I've thought about a GT4088 for my own Supra. Garrett recently upped their prices across the board and while they are very nice turbos I personally believe the noticeable but bearable difference in lag (a couple hundred RPM at most) wouldn't be worth $1000+ to me. A T66 as I described would cost in around $900-1100 depending on the source, the turbine, turbine housing style, coatings, etc. A full dual ball bearing one would still undercut a comparable GT by several hundred dollars.