I think with the 1975 because you get the knee control, you can really shape it more than the others. The 1980 is good, but 1975 seemed more aggressive to me. That said when I tried them out I wasn't using them on the 2 buss, I was using them on tracks, so maybe there the 1980 will work better?
With the CSP you get the input stage (which is basically like an EQ filter of sorts), but that also affects the key input of the compressor. Also the CSP compressor has the all important knee control, and various different auto-releases (based on different compressors). With all the URS compressors it really makes you learn how to use the attack and release properly - bear that in mind if you aren't getting the results you are looking for right away.
Oh yeah, and I know you said you didn't fancy demoing them, but why not - if you are looking for something punchy just try out the 1975 and 1980 and see which one works for you. Even if you don't trust your own ability picking 1 out of 2 can't be too bad. Also there isn't a HUGE amount of difference between these compressors IMO.