It varies greatly. I think it is officially up to 21Mbps, but in reality you'll be lucky to get a tenth of that. The only way is to check with your network. If you get any HSDPA access, it will be better than 80Kbps!
It's HSPA+, which is HSUPA and HSDPA combined, and somehow it results in a ceiling of 21MBps download, 5.76Mbps upload, those speeds cannot be actually reached, but either way, the HSDPA that phones have had for years were rated with a ceiling of 7.2, so this is faster on paper as a start. (I guess you could say 3x faster than just 7.2 HSDPA).
I think it will be faster again once LTE is rolled out In America?