I have a 2010 370 with about 20,000 miles on the clock. In Australia, there are stacks of V8 GM sedans making bulk power 400HP+ at the engine, and the 370 just wasn't quite cutting it at the traffic light 500 anymore
So after a lot of research, I see the general concensus among FI 370z owners is that the GTM kit is superior to the Stillen. I daily drive the car, so I am going for reliability over peak power. I enquired on GTM's website last week about the viability of this kit for RHD, and a bunch of other things, and to my suprise I got an international phone call from Sam @ GTM that evening on my work phone. I was impressed, and he spent a fair bit of time with me explaining my queries/worries about the kit.
I placed the order Sunday night. There is about a 3 week lead time on the kit I hear.
I'm doing the install myself, and will probably set it up with water injection as well (as I have an old Aquamist kit from my previous FI car).
Watch this space for the build/outcome! Hopefully all will go smoothly.