I think I was talking more about driving dynamics (mostly in a track or auto cross situation ie driving the car at its limits or close to). when just driving around town and stop light to stop light I agree there is really not much difference. But in an aggressive driving situation my 200hp 99Si or 220hp 2010Si behaved nothing like my 256hp S2000 or like my 400hp EVO X or like my friends 396hp SC'd S2000. They were all very different experiences.
FWD Layout - The 99SI would pull you around the track and during high speed cornering would tend to oversteer and would then start to understeer as the tires heated up. During low speed corners it would oversteer stronger and when the tires were very hot it would understeer bad. Acceleration was good with the exception of TQ steer here and there. It never did anything you didnt really expect it to. The 2010 Si was a lot more neutral then my older Si but I had more fun in the older version the newer model had a very boring 1st gear that just feels wrong for the engine its (much to long) to make the car fun it really needs a final drive or boost imho. It can be driven fast around a track (I dont use 1st gear on tracks so it was a non issue and 2nd, 3rd and 4th gear feel good in it) it did not exhibit some of the understeer issues I had on the older model. One thing I hated about it is the braking when the car would have traction issues during braking the pedal feel would get weird and inconsistant (not from brake fade though).
AWD Layout - The Evo X was by far the fastest around the track and also the most boring the car simply does too much of the driving for you, go into a corner too hot (within reason) and just turn the wheel and stay focused and dont freak out and the car finds a way to get you through it, braking was excellent and the car while being pretty neutral during some corners it tends to react a little bit like a RWD and the rear can actually step out a bit, which I never experienced in the Evo 8s. Biggest downside is the stock clutch is crap and should be replaced upon taking delivery of the car.
RWD Layout - The NA S2000 for me was the most fun the car it was a blast to drive around the track. It was exhilirating and if you pushed it too much it would bite you in the rear! The more you drove it the better of a driver it made you it was predictable with the write tires and though it could have used a little bit more power or a final drive it was by far the most fun car I have driven. The 400HP S2K required a lot more restraint specially during corner exits, get on it too much or too early slide and spin, though after a little while of driving it was fun and on the straights it was a beast. It just felt like too much power for the car (unless youre into Drag racing) maybe would have been better suited for less technical track.
Remember there are tons of different types of drivers and people who prefer all different layouts. Given time and resources to use different suspensions, settings, tires and go fast parts you can get most cars to behave however you want in most situations, Ive seen FWD and AWD cars drift Ive seen RWD and FWD cars Rally and so on... but all the drivetrains being not too much different I disagree (at least in my experiences).
In the end will people cross shop the two cars, I am 100% positive they will... It just doesnt make a whole lot of sense to me but my goals and what I intend to do with the car are probably different then 80-90% of the buyers. I will track it, I will auto X it and I will modify it with function in mind over looks (though i am sure it will look good too...LOL!!!)
I am not a professional driver just an enthusiest and If I were i could probably give much better descriptions, but these are some of my experiences with the different drivetrain layouts - sorry for going of the SI vs FRS/BRZ topic a little
