For a while last year I ran an old 42T small Biopace with a 50T round ring on one bike with downtube shifters, and the usual Biopace 52/42 on another with 7-speed brifters. No problems after getting the front derailleur adjusted a bit. I dropped the chain a couple of times, but minor tweaks to the FD sorted it out.
The Biopace were more eccentric than conventionally oval, but the smaller Biopace rings were more elongated than the 52T, which is only slightly out of round.
The small Biopace ring *felt* better on climbs, but I can't claim any consistent differences in speed/time. We don't have any climbs long enough to matter, maybe a mile or so undulated from 2% to 5%. It just suited my choppy cadence.