I realize that transfer rates across the Internet diminish significantly with latency, but what's the good answer for someone shrunk down to <10Mbps when the smallest pipe between them is 100Mbps and latency is <40ms?

Without window scaling (RFC 1323) your max transfer rate at 40ms RTT is 65535*8/0.040 = 13.1 Mbps. So slightly less than 10 Mbps isn't too unexpected. Steinar Haug, Nethelp consulting, sthaug@nethelp.no