[Lmn55d]

I would call. You most likely get 2 BB on the river if you hit your straight and you should call if you hit an ace. He could easily have an overpair other than AA here. I'd say you have 5-5.5 outs on average with solid implied odds.

Edit: I'm pretty confident your implied odds if you hit a straight on the river are somewhere around +1.5 BB. If you hit an ace, it's probably around neutral, possibly slightly negative or positive...we'd have to do a Bayesian analysis of the hands he caps preflop, bets flop, turn and river with to see how an ace hits him on average. He's almost never folding though.