10-25 NL middle set at the RIO

[Bellagibro]

Effective stacks are $6200. I have been at the table for about an hour and villain just got back from a dinner break and we only have about a round and a half of history together. He's pretty young probably about 22-25 or so and like most young guns, aggressive as far as I can tell.

Mississippi Straddle is on and he raises first in UTG+1 after both blinds folds to $200. One cold call in middle and I cold call in cutoff with 55. Button folds.

Flop ($685) As5s3h

Villain checks, CC checks and I bet $300. Villain raises to $800 and CC folds.

What's your move?