From the Edmunds write-up:
To get that 350-hp rating, Nissan revised the ECM tuning of the VQ37VHR engine and fitted a less restrictive exhaust. The exhaust pipes are laid out in an H configuration for the Nismo 370Z instead of the Y-pipe on the regular Z, and have, of course, been tuned to deliver a deeper sound.
The 350 hp peaks at 7,400 rpm versus 332 at 7,000 rpm in the normal Z. Redline remains 7,500 rpm, though, so you'll really have to work to use that extra power. Torque edges up 6 pound-feet to 276 lb-ft at the same 5,200-rpm threshold.
The part about the ECM tuning is great, as it means that there are gains to be had from tuning. I'm sure UpRev can do an even better job than whatever Nissan/Autech did as far as a tune goes. I'm really not all that impressed with the hp and torque gains, however, especially not when you have to rev all the way to 7,400 rpm to achieve that peak hp. Bottom line is that as far as hp and torque gains are concerned, there's nothing they've done that can't be done better with parts from other aftermarket suppliers such as Stillen and UpRev. Don't get me wrong though, I'm not trying to knock it as a poor effort or anything like that. I applaud them for actually bumping up the hp on this variant vs. having just suspension and aero upgrades like they did on the 350. I'm just saying that if you're looking to squeeze more hp out of a 370, there are more effective ways to do it than plunking down extra coin for one of these. On the other hand, if you're all about suspension upgrades and chassis rigidity, getting one these might be the way to go.