This is going to depend solely on your location and the signal strength you get in the area. If your using VZW service you are going to need a more accurate reading of your signal before your try and connect via tether (can save you hardship and money in the long run)
Dial ##DEBUG (##33284)
select Debug Info
Choose HDR (for data/EVDO signal) (1X for phone signal)
look for Rx Power and check your -##dbm
The higher (technically lower) the number is the less signal you will have in the area and the more chance your speeds will be in the toilet.
-95 and Lower (technically higher) will give you a connection albeit not a good one. Very good would be -80 or lower (technically higher) if its in the 70's you will have speeds of a between 1 and 2 mb down and 200 to 300 kb up. which in my case I had -77 dbm.
since it is a phone your signal will flux so you are going to want to make sure your in a area that you will steadly be using the phone/modem and check the signal at that location (indoor coverage is normally way different from outdoor so head closer towards a window for best results.)
GL hope this helps
Speakeasy.net/speedtest (connected with XV6850 Touch Pro tethered)
Last Result: Atlanta GA (from Upstate SC)
Download Speed: 1325 kbps (165.6 KB/sec transfer rate)
Upload Speed: 314 kbps (39.3 KB/sec transfer rate)