Download speeds depend on the hosts & what speeds they're offering/have available at the time.

A internet connection of 3 mbps = 3 mbps - about 20% overhead / divided by 8 to give you bytes per second. So your total speed would roughly be around 300 KB/s. BTW overhead is loss of speed due to distance from supplier, quality of cabling, loss due to connection devices, computer set up.

These links should answer you about speeds (a) What speeds are T1/T3, etc. for LW, __ (b) More on LW connection speeds,
(c) What is a T1?. IMHO you will do best with a T3 setting.