Gamma1734 Modern PC's can handle very low latencies, I think I can push it down even to as little as 8 samples (with triple buffering though). I read somewhere, that 64 samples might be the "golden" setting.
My RME BabyFace Pro is limited to 48 samples and that generally works OK on my old Dell laptop with Garritan CFX. A desktop machine will run better with fewer dropouts than a laptop principally for the energy management I think.
I think most of the studio RME units were limited to 32 samples. But maybe there was one top of the line unit that went lower.
If you look at the pro audio forums (gearspace), engineers don't seem to go below 64 samples; they are running specialised computers and interfaces, lots of tracks, and generally less concerned with latency. I have see a couple of guys post that they can run 32 samples, and one guy post that he got his system to work ok at 16 samples.
All that said, the ecosytem latency is really what we care about (key-to-eardrum). Reducing the sample settings becomes increasingly inmaterial in the whole scheme of things (e.g. 512-256 is a much bigger change than 64-32 samples).
The easy reduction in latency is to change from speakers to headphones, which could buy say 3ms, depending on one's setup.