Barefeats have updated their benchmarks to include a 17" model. Looks like the 8600M GT is clocked a little higher in the 17" models. Perhaps not to the same extent as the last generation though, I'm not sure. The difference here seems to range from "barely noticable" to "noticable...maybe".
Interesting. I wonder what the exact clock speed difference is? Could be another excuse to get the 17" model-except I have to admit, I'd feel better about the theoretically longer lasting LED backlight in the 15" model.