I've tried both, and a couple years ago I would have said Nvidia with that TNT2, but now ATI has been giving extra power, and not cheating people on features (directx7 built-in to modern cards?!?!?! COME ON NVIDIA!), while keeping prices down and usually the form factor is better (nvidia sometimes puts HUGE heatsinks and cooling fans on their cards). Also, if the X850XT can actually compare to SLI, that says something good about ATI or really bad about SLI (Nvidia needs to completely reinvent SLI in their 2nd generation, there are WAY too many bugs in it right now).
Oh yeah, and about that CCR vs. Viper, as much as I hate exotics and love american muscle, the viper doesn't stand a chance to most euro exotics. I thought the Bugatti Veyron was the fastest, but that was a couple years ago, maybe you're right. It's also spelled lamborghini.
That analogy is fine though, top-of-the-line vs. top-of-the-line. If you're talkin mid-class overclocked maybe a KB Mustang vs. a turboed Z06 Vette, or low-class overclocked that don't do crap when it comes to new games, you could compare some jap crap ricers to each other like a supercharged, (OF COURSE NOS'ed) Evo vs. a NOS'ed, possibly NOS'ed, maybe even a NOS'ed Eclipse. And if it's a low-end overclocked gaming PC, you could compare the same cars with ground effects and maybe NOS'ed engines (or NOS'ed) with about 400 tv's in them and, how could I possibly forget, a 40" exhaust TIP (that's gotta add about -5 horse when you count the drag and sparks on the ground and the large fruits being thrown into it constantly), that's like a mirror image for cars vs. computers.