In the interest of me not writing an essay here is a second post with a small explanation of radios:
All the radio does really is controls the way your phone authenticates with the towers. Radios either work or don't and there isn't much in between. The only thing that I have noticed with a non stock radio is that it takes the phone 3-5 extra seconds to update the animation of the bars of signal strength.
A non stock radio not working for me was - suddenly my phone moved into roaming mode and asked me to enable roaming because I did not have data - this happened at home where I usually have very good coverage as I am able to see T-Mobile's tower across the lake.
I would say just do a little experiments - to the best of my knowledge is ok just make sure you read the remarks on the stuff you are flashing.
One last point always have the default rom and system image (the one Atmazzz has in a really nice post of how to revert back to gingerbread which he did not want to sticky

) just in case something gets screwy and you want functionality when you are around your computer as it requires Odin.
Hope my long essays helped a little