I use GnomeBitTorrent and I get 100 kb/s regularly on a 1.7 Mb/s connection. It's a very minimalist BitTorrent client which a very simple interface and no bloat.
I like it much better than Azureus, which, I must say is nice too, but a bit resource hungry.
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I am very impressed by Azureus traffic shaping on the Mac, it seems to be an excellent BitTorrent client, aside from some minor issues you may experience. I also like being able to throttle down the upload on a particular file, because that generally de-prioritises it. But watching the traffic shaping on the Statistics window brings me peace and joy, when i see it blasting at that 40kb/sec* i know i'm getting my broadband money's worth Also the global upload capping is good to keep the uploading traffic about 2/3rds of the global download speed, as is recommended by the BitTorrent gurus.
*not fantastic for some of you speed whores but i'm sharing broadband with my neighbour and i want to leave headroom for my own surfing, isync, mail, etc. (my broadband promised by telco as 1mbpsdown/512kup but real numbers are probably half-ish of that)