I've got over 1MB/s (ie > 8Mbit/s) with transmission on my N900! It was one of my 'wow' moments with this phone.

I've noticed that when the initial piece of data comes through for a large torrent, the N900 gets -very- unresponsive for quite some time. I think this is due to allocating space up-front for the whole file on the FAT partition (which doesn't support sparse files like a native FS would do). I just leave the phone alone for a couple of minutes until it sorts itself out.