Bluff, Bet Size

[theBruiser500]

HU vs. someone forget who, take his play at face value this hand. if anything he is slightly loose caller. he raises to 300 in SB (so actually 3 way), i raise to 900 in BB with 98s. he calls. flop is (we have 10k each) T74, he checks i check.

turn is 5 putting 2 spades up, he best $1000 i call. river is Ao, pot is 3800 i have about 9k left, he checks i think i need to bet here (anyone disagree?), what size? considered overbet, pot, and smaller bet sizes.