Well  I've had a Toshiba M205 for a couple of years now and must say it rocks for 2d tho I haven't installed any 3d apps on it so can't comment about how well it performs in that area. Anyway it's got  an nVidia 6200 go grahics card so don't think 3d would be much of a problem depending on the program. Screen brightness is no problem and the pressure sensitivity is not an issue for me. Not sure what Toshiba has for newer tablets but at the time I got the M205 it was the only model with a dedicated graphics card.

About the only other brand of tablet pc I've heard mention of for artists is Motion and they are a slate not convertable. You might want to check out a few Tablet specific forums such as
www.tabletpcbuzz.com/