I switch between an older road bike with 1980s style aero brake hoods -- just rubber covered hooks -- on 42cm traditional bars and downtube shifters, and another with brifters on 38cm compact drops. One has traditional circular chainrings and 172.5 cranks, while the other has Biopace and 170 cranks. Always takes a few minutes to adapt if I haven't ridden one or the other for awhile.

The bikes are pretty similar otherwise but it doesn't take many differences to make them feel very different at first. Some rides one feels familiar and some days it feels like a stranger's bike. But it's all good.