Currently Cavs are 31-4 and Thunder are 30-5.

That is a combined 87.1% W. Extrapolated to 164 games, they're on pace for 143 wins (technically 141, since they need to play each other 2 times)

In 2015-16 the Warriors (73-9) and Spurs (67-15) combined for 140 wins and just 24 losses.

Will the Thunder and Cavs match or beat that mark?

If for some reason, they do not play 164 games, it will resolve to a probability based on the assumption their win pct is the chance they win any unplayed games.