Let me preface this with I work at a Radioshack.
When we first got the G2's in, before the phone actually launched, I tested one out just to see what kind of speeds it could get. My store is in a 5 bar HDPA+ area. The first test out of the box I got 8mpbs, and the second I got 10.5mbps, every one after that was ~10. After the phone launched and a few weeks went buy I got mine and iv been getting between 4-7mbps in the exact same spot.
So the phone is capable of it, but now that tmobiles network is getting more hammered by HSPA+ phones its slowing down I think.