I think you said it best yourself. SB will have way more 2's/5's in their range, potentially a 34, A3, A4 draw as well. You basically played it exactly like an Ax, I think if you had an overpair you would be more likely to shove pre flop with your stack size but maybe that's just me.

I see the SB flatting range not so wide, so he will have as many 5x as you have. He might have 54s and 65s than you not, but he probably don't have A5o for exemple, and you do (Actually I raise 65s from CO too). I also think the SB is whole lot of overcards such as suited broadways, and pockert pairs.

Said that, I think you better cbet flop small and check this turn in order to get showdown or bluff catching river, I don't think you get folds from better hands on this turn (maybe some AT he didnt 3bet, or 33). And the villan might, at least should have some leads bluff river after check-check turn.

I would keeping barreling with those no showdown hands and the ones that get some equity on this 8 turn (76 and 97 if you have those in your CO raising range).

See you!