Valve already optimized their game engine, which I think they know A LOT better than NVidia in the mixed mode. NVidia could have reduced precision even more from FP16 by using FX12.
Frankly, I would not be the least surprised if NVidia used clip planes. Quite a few people (Hellbinder,Uttar come to mind) know that NVidia is doing much much more dirty work in drivers than we even know. When the whole Tiger Woods shader subject was brought up.... Catalyst Maker said something along the lines of... 'so this has finally been brought out'. ATI knows very well what NVidia is doing with their drivers and in what games, yet they don't come out mudslinging and accusing.
Valve better damn well declare an all out war against NVidia. Driver IQ hacks are bad enough, but the line has to be drawn on static clip planes. NVidia had enough money to force Futuremark into a corner, but its not going to work this time. Using static clip planes to inflate specific timedemos for marketing your POS cards is fraud. Its as simple as that.
I sincerly hope that they won't even CONSIDER doing that. I have a gut feeling that Anands numbers come from either DP/BB, and hes publishing them to deliberately put NVidia in a good light. Either that, or he's setting NVidia up to screw them over once the real thing is out. Once HL2 comes out, and users can make their own custom timedemos --- and we find out that static clip planes were in fact being used, then NVidia is in deep ****. Valve has the backing of gamers worldwide, and if they step up to the plate like they did before, other game developers are going to come forward as well.