How accurate are Good Faith Estimates?

I was asking cause I told my loan officer that I would want to at 800 mortgage payment a month. She told me I would be looking at FHA of 100,000. Includes (Principle, Interest, Mortgage Insurance, and Property Tax).So yesterday I received one saying I could get 114,000 and my payment would be 707 per month. (Principle, Interest, Mortgage Insurance) at 4.25 over 30 years. It's this accurate? Because I have been looking in the range of 75,000 - 100,000 to keep that 800 or lower mortgage. However if I can get more house and a lower payment that would be GREAT! I'm going to talk to my Leander Monday, I just wanted to get different opinions as well.

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