Are you aware that there are new notebooks/tablets with Thunderbolt ports being released? They make it possible to have a thin-and-light for on the go and will soon see docked eGPU enclosures courtesy of MSI's GUS-II or BPlus TH05.
I'm keeping a list of Thunderbolt-equipped notebooks in the thin-and-light link in my sig. A 14" Gigabyte U2442N (GT640M), 14" Lenovo T430s (NVS5200M) or 15" Macbook Pro (GT650M) have a dGPU and 900P+ LCDs so could meet your requirements as standalone units but also offer a Thunderbolt port to give higher performance docked graphics options. The 15" Macbook Pro with a high performance i7-quad CPU but unfortunately is outside of your budget.
I thought Thunderbolt ports were just a type of USB port? How would that affect physical specs of a laptop?
So with the new Dell XPS 15 being released today, I'm almost sold on it. However, is there any reason to wait until the end of summer? Is a pricecut and/or tinkering of the product likely to happen in the next couple months?