[mmcd]

On third in these type of spots, I'd rather cold-call than 3-bet. I think keeping the pot size under control and leaving yourself flexibility on later streets is more important than trying to isolate the guy when you're probably not much better than a coinflip. Your 5 vs. his 8 in the door will allow you to force him into a lot of incorrect folds on 5th and 6th depending on how the boards develop, and depending on how he plays, you may get paid off pretty well in situations when you both brick off. Think about it this way: With the pot bloated on 3rd, how likely is he to make an incorrect play later in the hand? How likely are you? On 4th here I'd just call and see what falls on 5th. He's going to put you on a strong low peeling a card, and will almost certainly bet again if you both brick, and you can get out cheap if he hits something ugly.