yeah, a lot has to do with the server.
I like the speedtest.net server in washington DC... seems to be pretty consistent.
I think if you were expecting 2.5mbit over 3G, your expectations were a little off. 1MB is pretty average for EVDO (verizon EVDO speeds tend to hoover around that as well).
As for wimax speeds, they differ GREATLY depending on the area. Clearwire really didn't do the best job deploying the network (they were in a hurry and had limited funds).
I would wait for sprint to "correct" the wimax via network vision over the next ~6 months. You will also see 3G speeds increase in the next ~6 months as well.