Welcome to FT!!
If you have no problem flying out of IAD I would strongley recomend UA MP. It is about a 50 50 shot they will Match your US status because they are both in the *Alliance. It never hurts to ask though.
But your US Gold will get you E+ all the time if it is avalible. Doing the math if you plan to fly 75,000 a year and you made the Switch to UA on monday you could reach 40,000 miles by year end and if you put in some F fares and Y fares you will get 50,000 EQM which will get you 1P status (Mid Tier).
I hope this helps.
Ben