i dont like the all in on the river and here's why:
You said you were putting him on a flush draw, like yourself. Well, if he's on a flush draw the odds are that he probably is drawing to a king or ace high flush. I dont know many people who would chase a flush draw with a low flush card (except maybe kaart

). Here, if im thinking flush draw, which is what id be thinking, i would check the river, as odds are you're only getting called with K or A.
Plus before going all in, the pot is 6400 chips give or take a couple, for 2000 more with second nuts, I am definately calling there. Especially, since if he loses, he still has 4300 which is higher than the average stack.