99 overpair facing all-in

[TheDrone]

Full Tilt $10+1, 30 left, 19 pay.

I have the second biggest stack on my 6-handed table with 24k. I have been playing very few hands, and my raises have been getting respect. Big stack (34k) has been playing somewhat aggro but has not been dominating the table or anything.

Blinds 500/1000 ante 100 (I think)

Hero is UTG and raises 3x with 99.
Big Stack calls in MP.

Flop(8.1k): 3-5-5 rainbow
Hero bets 5k, Big Stack pushes, Hero?