If people bother to submit them (not everyone does), Sensorly also has speedtests on the map within the application.
Looking at the app for T-Mobile LTE in San Diego, the typical speed test appears to be in the 20 down / 20 up range. There are a few outliers as high as 45 down, and a couple as low as 11 down. I encourage you to download the app yourself and explore it (and maybe upload some data for your current carrier in the meantime so others have good information to base their decisions on - I love Sensorly!)
Switching to 3G (Sensorly does not acknowledge HSPA and HSPA+ as "4G"), I'm seeing data in the 5 - 13 up / 2 down range.
I'm AT&T and on the other coast, so I can't attest to the accuracy of the tests I'm seeing. But I've found the coverage maps to be reasonably consistent and I submit speed tests on a regular basis, and they always seem to jive with my actual experiences.