there use to be a "rule of thumb" that if you multiplied the power by 4 times you doubled the coverage. The AM class C's are usually 1 KW affairs. 5 KW should cover twice as much area assuming assuming the B is around the same frequency. This example is not a Cumulus station but maybe explains why a class B would be better than than a C for powering a translator. 1310 in Chattanooga (5 KW daytime) was delisted a could of years ago. 1450 WLMR with a COL of Chattanooga too has a "small" translator footprint:
http://radio-locator.com/info/W277DA-FX
If 1450 went 5 KW on 1310 daytime they should be able to "double" their translator coverage assuming there is "room" in the FM spectrum.*
* This is not an engineering study and your mileage may double.