Last Sunday I flew a typical GA IFR profile from Kortrijk (EBKT) to Deauville (LFRG) and back: climbing as fast as possible with a non-turbo single engine piston through and above the remainders of a cold front (and picking up just a slight bit of ice). Climbing to FL120 in the going and FL150 in the return. All on Mountain High oxygen. Airplane is a Robin 3000/160.
It works and it is very rewarding ! Impossible without IR, and higher risk without oxygen. Attached video my son made (some comments in Dutch).