The Gringo Maximilian figures are quite tall but so are the Foundry Mexicans! Most of the range has been sculpted by Mark Copplestone I believe and his figures are nearly always really big 28s.
So yes, I wouldn't hesitate to mix the Foundry Maximilian Adventure and the South Of The Border figures with the Gringo ones. Mind you the latter are superbly sculpted, so there might a slight edge in quality, but not too much.