Tested the demo on my PC. Dualcore AMD @ 2.2GHz with a 7950GT and 2GB RAM running Windows XP. Slower CPU than the iMacs but faster graphics card.
1024x768 with
High Details had some rather bad frame rates. Especially in places with a lot of effects, or when I moved around in bigger places. Could occationally pause for a couple of seconds.
Have to stay I wouldn't enjoy playing through the full game at this setting, though I did manage to get through the demo.
Looked pretty nice though, except for the low resolution.
1680x1050 with
Low Details was playable. It wasn't perfectly smooth, but I kinda got used to it. The difference in quality compared to the High setting was noticable (to me), but probably isn't such a big deal if you haven't played it High before.
Some stuff from the README:
BioShock is optimized for dual core machines.
For best performance, we recommend a dual core processor and either a Nvidia 8800 or an ATI(R) Radeon(TM) X1950 or 2900XT equivalent card.
BioShock requires support for Pixel Shader 3.0 or higher to run.
It also mentions some known problems with framerate stuttering on NVIDIA cards, which might have affected performance in my test. Some new drivers will be out today which should fix it. Or not. Don't know if it affects the 79xx series.
I'll see if I can get fraps running for some real frame rates...
Edit: Ran it again @ 1024x768/High Detail. Was better this time, in that it didn't have the pauses, but still wasn't smooth. Fraps reported framerates of around 20-30 fps, though it certainly felt slower and I'm not sure if I trust it. Or maybe I'm just overly sensitive to sub-50/60 fps.
Also tried at 1680x1050/High Detail. Max 15 fps and 2-3 second pauses. No fun
