It can go up to 10mbit. I get near enough 10mbit speeds almost all the time on my NTL connection. 10 megabits is the equivalent of 1.25 megabytes so approximately 1250KB/sec is the theoretical maximum speed.
As for upload speeds - I presume you're talking about cable? On Blueyonder the upstream on the 10mbit package is 384kbit so that's around 45KB/sec. On NTL it's 512kbit so around 60KB/sec.