Anywhere in the 40K/sec range is fairly standard for most US ISP upload rates. Multiply by 8, and it's about 320 kilobits/sec. Rounding up for packet overhead, it's most likely a 368kbit/sec cap.
You can always try out speedtest.net and see what you get there.
If you need a faster transfer speed then you should contact your ISP about a faster plan. Roadrunner Turbo, offered in my area brings the upstream to 1Mbit, 70-100KB/sec.