T1 maxes out at 150 kilobytes per second, so 766KBytes/s is actually... pretty good. Or maybye you have something else. Not to mention, the point of fiber is often distance and noise-immunity rather than bandwidth. So you still haven't really given much info on what your connection's rated for, sadly.
I'm guessing compression wouldn't help much unless the file is very repetetive, or the transmitting system very fast CPU-wise. However I have found compression useful under some situations(generally in combination with the
udpcast multicast tool, with which I've been able to achieve 99% of rated speed on a TCP/IP link -- at the expense of all other traffic on the link however
).
lzop in particular is designed to be realtime compression.
this thread on google groups shows a few tips. Window size is apparently important.