Depends on the bandwidth alloted to you by your ISP. Normally upload speed is capped at around 40kB/s. Because its capped at 40kB, you will upload to them at that amount regardless of their download speed.
You can always head to
www.speedguide.net for tweaks and patches to improve your speed, but you'll never go over your capped upload - unless of course you uncap your modem. If you do that, you'll have some FBI agents knocking at your door

.