From what I've read some others have had success with it & not been back to complain. As far as socks 4 & 5, yes they're a little different. 5 allows a broader definition or something. See http://www.clipcode.org/messaging/socks.html

I'd suggest you keep trying. I believe that proxies for socks 4 & 5 are different.

If you have doubts about those ones, google for more.