I'd guess that the 7900 Go isn't going to be far off that 2500, likely 550 core speed give or take 50 and probably 650's on memory and 512 of the memory. 512 is more of a numbers game than any genuine return "right now" but sales loves the numbers game. The real caveat I see is that they can't really clock these things even close to the 690 or so of the desktop parts. Back at the time of the 7800, you were only 50 mhz to 75 mhz off the top desktop parts which is what made the 7800 Go GTX so wonderful. I believe, from a power basis, that they won't get so close in the 7900 Go GTX, probably a lot closer to the GT version or the eqivalent of the desktop full 7800 GTX in the oc'd models.
The blessing they are willing to bestow in paying for what is a small step up, is probably that you can hope to put a G80 Go in it later on (worthy in my opinion for paying now) and upgrade to a Merom when that's available. Those two are pretty much good enough for me. But do bear in mind you aren't going to watch someone post in the forums that their 1710 is getting 50% better framerates than the 170.
I'm happy that Dell is supporting the upgrade pattern of GPU's in at least the top end gaming notebook. GPU's get outdated faster than the rest of the system and I happily expect to read in 2007 how people are still gaming high end on their XPS2's and 170's. If they are lucky they might even have an upgrade path the the G80 Go also, and that will prompt another wave of "oh they are out of upgrade boards what will I do" comments...
So deal with the facts that this notebook will be great, but not stunningly better than the last model. The entire series has given us a great upgrade path and long hours of gaming. I'm waiting to read people wearing out their keyboards next
And soon the 1710 will usher in the next step up, and a path that takes us straight to Merom and 64 bit.
Gamers who need a mobile solution have honestly never had it so good. It's not perfect, but it's a marked step up from where we were a few years ago.