I agree with Ben: The noise from 4000 revs (and Ben and I compared this a while back) is much nicer than CUPs or RSs. It reminds me of a 2.0S, or 2.2S howl, for those in the know [
] Also, the combination of grip from the fat rear tyres, the nicely sorted rose jointed stiff, dual-spring suspension makes the car very stable compared to the 964 RSs and CUPs.
It is true that you do feel you are driving something very special. Listen (again) to this noise [
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http://www.youtube.com/watch?v=SMbAN6nDuQ0
However, a reasoning similar to Ben's made me sell mine (just after restoration) and buy a 993 CUP. I thought that going to a 964 CUP (though I love them and almost bought Herr Schmitz Kermit Green 964 CUP) would be a big step down in bhp and I drive mostly at Spa, a bhp track! I was also very tempted by the nice GT3R now (and then) for sale at Gmund but was persuaded not to by people who ran them $$$$$$$$$!!!
So, after 4 tracks days at Spa with the 993 CUP, setting up its chassis and adjusting to a 6-speed short box (the RSR had a 5 speed short box), the main differences that I noticed are:
1. The 993 CUP engine is "safer," with a lower usable rev range and not as free reving as the RSRs past 6000 rpms (CUP is very similar in feel to RS engines).
2. The noise is more intoxicating in the RSR.
3. The RSR is more stable in all aspects of a curve (sharper entry, steady-state and more stable exit)--though I have not yet driven the CUP on slicks, only Michelin CUPs, so the comparison is not entirely fair but I doubt that I can better the grip of those 305 slicks at the rear!
4. Top speeds are very similar (the short 6-speed box helps a lot on Kemel, where I have the same top speed in both cars).
In short, the 964 RSR and 993 CUP are closely matched at Spa, in terms of performance. In terms of feeling special, the RSR definitely wins.