I had to make the same decision and bought the p105. The 3d marks seem good to me as you can see in my review of it. The big plus with the Toshiba is customer support is better, and the case design isn't nearly as futuristic/tacky.
The finerprint ID reader is cool too. It's also lighter, thinner, and runs cooler. But the Dell is probably like 1000 3dmarks faster. Oh it's also dual core.
If you just want to game the Dell is better. If you want it to be very good (but not best) at gaming and portable, then the Toshiba.