Pushing vs. pot-committing with 2 pair

[parttimepro]

5th hand of a 109 STT at Party. I get JTo in the SB. 2 limpers in early and middle position. I complete and BB checks.

Pot is 60. Flop is QJ3 rainbow. I check, BB checks, EP bets 30. MP calls, I call, BB folds.

Pot is now 150. Turn is T, completing the rainbow. I check, EP thinks for a while and bets 75. MP calls. I raise to 500. This is my first question: should I have bet more to eliminate any tough river decisions, or is anyone who calls this basically pot-committed?
EP folds and MP calls.

So the pot is now 1375. River is an A, putting the four-straight on the board. I think for a while, and decide that I'm not going to fold if MP pushes. He'll push with a K, of course, but might check behind with a worse hand. So I push. Second question: should I have just check/folded here? Isn't an A about the worst possible card for me? It's really hard to think of hands he would have called down with that I beat now. AQ, KQ, KX all beat me now. Only something like Q9, Q3 are behind, and those aren't very likely.

[Raiser]

Hmm, I don't think you are going to get a better hand to fold on that river. I like the check/call line better here bacause you will sometimes snap off a bluff.

[jah0550]

I'd push on the turn. If you are going to bet 500(thus pot committing you on the river), why not go all-in on the turn? I am almost sure that no one has AK, the only real hand you have to worry about is QJ or Q10, which is very possible. The pot is already 300 when it is to you, so I'd push here instead of just raising 500. If you are going to put more than 1/2 of your chips in the pot, you might as well go all-in. Just my 2 cents though.