Remember when I am reviewing lender quotes, I have somewhat of a biased opinion. Since I'm in the biz, and that business isn't a "non-profit" organization, my input can be seen as an attempt to steal the deal away. Let's be candid about that impression up front. I can give general information, but specifics depend on a great deal more information than what come up in most posts.
Here's the 30,000 foot perspective:
Rates did not go up because the Fed stopped buying MBS's. Rates went up (about .125%) because of economic news. Since last week the cost of borrowing has dropped a bit. If you re-shop around today, you will likely be able to improve your terms. I'd say you might see .125% in rate or .5 point in fee improvement from what you have now. The problem is that with a 60 day escrow at some time during the sale period rates will move again. Does that mean you then should try to get a third lender? If rates drop by .25% you shouldn't try and find another lender, but try to re-negotiate the terms of the lock.
The "best deal out there" does not exist. The "best deal at this time" does. Ensuring you close on time, as expected, with market competitive terms is all you can hope for. Finding the right lender is in some ways more important than saving $600 of closing fees, or .125% in rate. Am I encouraging you to overspend? No. I'm suggesting that (IMHO) if rates won't be dropping back under 4.75% for some time, your rate spread is pretty narrow - 5.375 to 4.875. If you can get 5.0% and miss 4.875% at the last second when you close, you've still closed at a great rate, as expected, with minimal brain damage. That's in the long run the best deal you can get.
Cheers,