I think its pretty obvious that Any major speed Nvidia is gaining from the DET50 betas is primarily from not rendering any fog. As well as other detail reducing tricks. I'd be willing to bet its the same reason that performance is up in NFS and any other games.
To think they went on tech TV claiming they did not understand why Valve refused to have them used.
Not to mention they are still stating any HL2 benchmarks are "invalid" without them...