Doing postgraduate study in America isn't as easy as you think. It's expensive to live in America and they will work you like a dog.
Before I dropped out of an American uni to come to the UK, even as an undergrad I was made to do unpaid labor in labs and it was a horribly stressful and competitive environment.
The work life balance is horrific and doctoral students are paid very low wage stipends, pretty much minimum wage in some unis. The amount you are paid is often barely enough to scrape by in most cities, even for US citizens who are eligible for benefits if they fall into poverty. It will be even harder as a foreigner because they will expect you to get by on your own.
The workers rights legislation in the UK is much more equitable, making sure that people get paid time off, breaks, no overtime in most industries. In America those protections are out the window, and every PhD and postdoc I knew in labs was extremely miserable and worked to the bone.
I would not endure that simply for the opportunity to obtain a gun 10 or so years from now when you get a green card.