[toybux]

He can also push with diamonds here. I think that leading at the flop is the better line. If he's pretty straightforward, you don't have to double him up if he has a queen. Just bet your standard cont. bet size or just pot it. If he pushes, evaluate how likely you are to be good. If he doesn't push with draws, you can fold and save yourself the money. If he pushes with 56, the FD, or a made hand (55-88, A4), you can probably call getting the odds you have. If you make check raise all in, he'll probably fold A4, 55-88 which are the hands you want to be all in against. He'll probably correctly call with a FD (which probably has at least one live over, so you're pretty much flipping here) and maybe a straight draw, and probably never folding a queen. Thus, you let him pick if he wants to put $6 in and be done, or if he wants to put the rest in. This is bad. If you lead, he'll push with a much wider range than he'll call this check-raise because he think he might have FE.

Edit: Just saw the edit of the OP. Without the flush draw, calling and folding are closer and probably read-dependent. If you think he'll bluff push here, you can still call. But remember, a lot of the hands you are ahead of have more equity against you than you have against the hands you are behind. Two overs you're about 75%, straightdraw 64%, A4 80%. Any hand that has you beat will leave you with only 10% equity.