WiMAX *can* do over 5Mbps for some users. The challenge for all 4G carriers will be getting 5+Mbps for *most* users at a distance and with many sharing a site. That will take large backhaul at every site and mimo antennas in order for *most* users to get 5+Mbps. Until 4G matures, it will be hit and miss performance for a while unless you live within LOS of a site.
Where WiMAX currently shines over T-Mo / HSPA+ (and others) is that it is currently available in a few markets, AND is geared directly for data usage.
T-Mobile HSPA+ (AT&T HSPA, VZW EVDO, Sprint EVDO) are primarily geared at mobile handsets. WiMAX does have an advantage of being first out of the gate, and covering areas that many typical 3G carriers don't typically like to support (rural areas) as well as not having those obsurd caps.
