chaos,
Do the GMRS only handsets have better antennas than the FRS/GMRS hybrid radios? IIRC the FRS/GMRS hybrid radios allow more power on the GMRS channels while the FRS channels are limited to 1/2 Watt. But on a hybrid radio they share the same antenna so they would both have an antenna limitation.

Would going to a pure GMRS radio give you more power and a better antenna? The Icom IC-F21GM (pdf download) looks like a good radio. I wonder if it has the antenna limitation...