Sam,
I get the feeling you are over thinking this thing a little bit. Based on this and your other post you sound like you might be entering paralysis by analysis.
Mortgages while a big deal, can be refinanced! So if rates drop to 2% (HIGHLY UNLIKELY) you just refinance into the lower rate. The loan is over a long period of time. So maybe in 5 years your making crazy money/windfall and you are in a position to pay the loan off. Since you are here I am assuming there is a good chance you could kick the ass of nearly any loan that you end up getting.
For me I have a relationship with a lender, he offers decent rates, but he helps me get deals done. I dont care about 25 basis points on the loan if that means the difference between getting a house closed in 28 days versus not getting it closed.
Relax, walk into your bank or ask a friend who recently bought a house. Loans are pretty much all the same because they all end up being sold in the same place. So in theory the rate might by slight better at bank A, but might have higher closing costs then bank B.
The banks compete for your business my friend!
Good luck.