Just a couple of comments.
SRT-4 People are hitting 12's and 300whp on stock turbo and internals. 12's with 1K-2K worth of mods. With an aftermarket turbo the engine has hit 500whp on stock internals.
RX-8 It's awful slow in a straight line, once the engine is wound up it's not as bad. Like the Miata, on a road course it is regarded as one of the best handling cars out there and is very easy to drive fast. It will embarass a lot of cars around the track that are faster in a straight line. For you to say the engine has no potential you must not be familiar with rotaries. It's still a version of the 13B which mazda has turbo'd in the past and many drag racers use to make 7 second monsters. Ever seen a Starlet hold a wheelstand down a track, at 11,000+ RPMs, while running 8's, 9's? Most chances are it's powered by a turbo 1.3L Rotary. The Renesis is just the newest incarnation of the motor and very few drag racers are using it. It's a new motor thats in an expensive car, I doubt you or many others know the potential of this motor. Another thing you should keep in mind is that it was detuned in our market for emissions regulations.
350Z/G35- At 287hp, in a small 2 seater, its an embarassment that this car is barely a low 14 second car. Most times I've seen are in the mid 14's anyway. There is a guy around the way that has the Greddy Twin Turbo kit for it, but it's still not that fast. A stock turbo SRT-4 was neck and neck with him. The TT 350z isn't tuned but neither is the SRT-4. The nissan is a nice car with a good aftermarket, good looks, and decent athletics around a track, but it underachieves in my book. I blame it on these damn Turbo 4's! They are forcing everyone to pack some serious HP.
Audi/VW(Turbo's only) None of the 2.0T's are available in our market yet. A4's currently only have 1.8T's, and as nice as the 1.8T is, it's very limited. 250whp on the stock turbo is a myth. Even with the K04 from the TT, the most you'll see is about 225whp. I'm on the lightest platform(GTI) you can get a 1.8T in. It's the 180hp K03(s). On the stock turbo it's easy to hit 13's, if you want 12's you are going to have to drop some change(turbo kit) and the audi's are heavy. The S4 is a different story, if you can find the older 2.7L Biturbo you can build a beast out of that. The current ones come with small V8's but are still pretty quick, but very pricey. The audi's are heavy as hell and pricey and about the 2.0T's that you speak of. It's going to be a while before the aftermarket picks up on those. I would expect them to see them in the Mk5 GTI's before we see them in the Audi's. Also the aftermarket is going to take a while with such a new motor and considering the amount of time it took to crack the ecu for the 1.8T, I would assume the same for the 2.0T. One point I agree with you though, VW/Audi engines are built like rocks but nothing else seems to go right. Every one of these problems happend with less than 10K on the odo. My (03)GTI's 5-speed(manual) tranny went, my friends 03 GTI needed the turbo replaced, another friends 02 GTI broke an axle, and my friend with the R32 that he has had for a couple of months just replaced his head gasket. Plus VWOA is in financial trouble and their customer support is piss poor. They will do anything to get out of warranty work. Until the 2.0T is in a lot more cars and we can see its potential with the tuners I would stay away from it.