In the mid-to-high range, it all depends on what polys are used and how they're put together. I've seen (and built) 100k+ poly figures that work admirably on crap hardware in spite of itself. Poser and D|S are very quad-friendly, and can tolerate tris fairly well. What you don't want are a lot of nGons (polygons that have more than four half-edges/four points). nGons can swallow your CPU whole if you have them with too many sides and have too many of them on the mesh.

(Hint: If you make mesh, you should always - ALWAYS go over your result with a microscope and make sure you don't have any, or at least have a very good reason for having one. I remember one a long time ago that probably stumbled in a nurbs -> mesh conversion script, and it would up with an nGon that had 224 sides, but was positively microscopic in size. I found it when the render engine kept vapor-locking over that particular part of the mesh).

It is a number set that also changes over time. In gaming, Quake 2 pushed the limits with a 1200-poly mesh, but Q3 pushed the limits with a 3500-poly figure (IIRC... could have the numbers wrong)... it was all about what the engine could handle. Same in CG - back in the late-1990s, Dork and Posette, with 10-12k polys each, were considered pretty mid-range. Vicky was considered a CPU-slayer at 40k polys each (IIRC), if you had three or more of them in the same scene. Nowadays, that ain't jack for any Intel Core processor and a decent vidcard (w/ OpenGL scene rendering) - you can happily park 8-10 of 'em into a D|S scene (dunno about P7) before you see anything bog down.

Just my $0.02