My wife and I are looking at a variety of road bikes to replace our current cyclocross bikes. We will be keeping the old bikes at a weekend house. I would describe our riding style as quick touring. We will cruise along at 15-18 but rarely get up to 20 on the flats. we both are wusses on the hills and both ride triples on our current bikes. On steep hills we both frequent the granny. It looks like almost everything available in 105 road bikes are 50-34 compact doubles with 11-28 cassettes. So far we haven't really liked the SRAM (which we have seen with larger cassettes). My question - if we go with 105 do we have a lot of flexibility on cassettes if we decide we want more low end? Can we just swap in an Ultegra 11-30 or even a mountain bike cassette with more low end or do each of these things fit on different hubs or demand different derailleurs?