Yes, the radio does affect your signal strength. Try out the radio thread on the TP Upgrade forums. I tested around 6 radios and found out that the lastest Verizon radio works best for me area. Another member on this forum that I talk to occasionally had the Telus radio on his. To me, the Telus radio gave me the absolutely worse signal, even my stock Sprint radio was better. So yeah.. test out each radio and find the one that give you the nest number closest to zero
Also by having better signal, you have increased your battery life.
Good luck!