Mileage or pay!

I have about two hours left to be able to change this flight. To book the United flight using Chase card for 25,000 miles one way today to London but got round-trip for $928. What would you do? This is of course for economy. I am gold so I can book economy plus at booking, hoping to be able to get upgraded going through Denver instead of SFO or LAX which I think would give me a better chance thoughts?