i´m playing a roadster since two years now and i´ve tried the road king II - the only difference in sound was the powertube option.
i changed my tubes to EL34 in the roadster and i´m very happy with it.
although i was never really satisfied with the brit mode as well. gain wasn´t the problem, but to me this mode was lacking on low end and sounded to harsh to me.
so i switched over and turned up the gain knob on the tweed mode.....yes, this was the dirty ac/dc-like sound i was looking for.
now my clean channel is the yellow channel set to fat-mode and my dirty crunch sound is channel one set to tweed with gain turned up full.
it is a bit less gain than the brit-gain but to me it sounds way more organic.