I've played through Bioshock a couple times, but have sold it. So I downloaded the demo and did what you asked. I strafed left to right looking at those big red banners and even though it blurred up a bit I could still read it pretty easily.
My TV is the LN32A450 (6ms advertised) connected to a 9800 GX2 via HDMI.
I've actually tested for this blur (pixel response time?) before in Bioshock and other games to see if my
20WMGX2 was better or worse. It is actually a little bit better than my HDTV. Which I thought was odd.
Can't comment on Mass Effect; haven't played it yet.