Old post but Tygr what was you final decision?
I have the identical requirements except I'm looking for an i7.
My CPU does alot outside of gaming.
I went with a Lenovo X201 Tablet with the 2.13Ghz i7. It was about $2200 before tax and shipping, but it's a BOSS for playing games, considering it's a 12.1". It also has a multi-touch pen-compatible Wacom tablet screen, which is ideal for finger usage as well as with a wacom stylus for digital art. It also has an open interior slot and antenna connector for a Qualcomm Gobi 2000 WiMax/3G card, which you will probably have to install yourself, but it's compatible with all major wireless data providers.
As far as gaming performance, it handles Halo 2 and Orange Box games with relative ease. It gets a bit hot, and excessive effects cause it to stutter, but nothing major. I'm planning on buying MW2 just to see if it'll work.
If you have the money, it's WELL worth it, as it combines the tablet with the light gaming machine perfectly.