This question cannot be answered simply, but here's what I have to say:
If you think HughesNet's latency is terrible, chances are high that a mobile broadband card will not be any better. Cellular based connections suffer from a lot of latency, especially in the upload rate (transmit) side of it, which is equally as important (if not more so in some games) as the download rate (receive) is.
Your connection will be on the better end of the spectrum if you're close to a Cell Tower. Like, mere miles.
Your connection will be worse if you're far from reliable high speed towers, have sufficient physical interference for the cellular signal, etc.
Mobile broadband cards are great when you're in a pinch/away from home and have to get something done, but for a near-realtime experience such as gaming, you're likely to be unimpressed.
Do I have experience with it in gaming? No. I've used cellular cards for other applications, and if it can't even smoothly hold a low-latency SSH connection, I would not even dream of using it for gaming.
Now, using a wireless broadband account for Xbox Live is fine on it's own (Netflix, online apps, communication, downloads, other videos, etc.), but again, I simply cannot suggest it for gaming. There are to many limitations to the capabilities of wide-area wireless to really make it an enjoyable experience in gaming.