The Captivate does support full hspa+ speeds, however, att has disabled the upload speeds since the iPhone 4 has exclusive rights to that. Now you can flash a custom firmware that is i9000 based and take full advantage of the hspa+ speeds adding the upload portion. Perception 10.1 is rocking solid right now on my Captivate!
True, but I got it confused talking about hsdpa and hsupa. HSPA is still fast but HSDPA and HSUPA is what the phone actually needs enabled by default on ATT firmware to make it even better.