It's a little slow at work today, and I'm planning on watching the 12 hours of Sebring while rebuilding my Z motor this Saturday, so I went surfing for some news and clips and found this site:
http://www.fastdetails.com/
There are a bunch of clips there, but the best comparison one is labeled "Penske Porsche (P2) vs. Dyson Lola vs Audi R10". It's creepy how quiet the R10 is, especially considering it's a diesel. The clip of the Porsche coming off the rev limiter out of the pits is interesting, too.
enjoy,
Dave