Tried again just now and this is what I got:
Ping: 1024 ms
Download: 373 kbps
Upload: 867 kbps
T-mobile's coverage map does not distinguish between 3G and 4G, but it does claim coverage for my neighborhood should be "excellent." I suppose I'll try Speedtest some more when I'm in other areas, but as I said, I'm perfectly content with this thing's speed on the Internet.