sam,
any gk head i've tried gives me excellent tone. the only difference is in power and features. the 700rb was awsome when i tried it. i use two different heads because i want the swr to provide strictly bottom as it doesn't have the tonal range as the swr but gives a really clear botttom. also, by splitting the two heads with the morley pedal any effect i run throuth the gk, such as distortion, doesn't cancel out the bottom. i also can shut off either head with this pedal depending on what i am trying to accomplish. great flexibility. any other questions, i would be glad to help you with.
peter