I was at PAX and asked the guy demoing it the specs of the machine:
Core 2 Duo
8800GT
2GB ram
It was running at 1280x1024 resolution, surprisingly set to *MAX* settings. Formerly "Very High", now renamed "Enthusiast". High is now known as "Gamer".
Anyway, on that machine, at that resolution, I pulled up r_displayinfo and saw that:
High - game was easily running 35-40FPS
Very High - game was running about 20-25FPS
The important thing, however, is that that's faster than the first game, and it was fully playable even at that 20-25FPS. This was also on an ice-covered level, the type of level that killed performance in the first game.