Truth is no matter what you buy now, you will always want to upgrade the whole system in a fiew years at most. You will want the newer screens, solid state harddrives, Dual Core 64 bit, ExpressCard slot, Edge Wirelss and who knows what else will be available.
What I'm trying to say is no matter what GPU (if any) you can put in your system 2 or 3 years down the road, there will be so many other features that you will want to have improved. My advice is to buy what has the greates value at the moment and in doing so you will save enouh cash to keep upgrading to a whole new system once in a while instead. So what if it has been on the market for 6+ months when you buy it, you'll still have it just like everyone else who bought it when it was THE fastest system around, and for a much better price at that, and all the quirks have usaly been worked out too by then.
What it really boils down to though is the amount of cash you can burn and how important it is for you to have the newest and latest in 3d performance right away. I can see the thrill in having the absolute fastest without having to wait, but personaly I just wouldnt have enough $$$$ to keep that up!...
Ps. As long as there is Sager notebooks Dell is the absolute LAST resort.