See here. It'a just one point of view (I'd encourage you to seek out other reviews) but it looks as if the R7 is a decent card (and, btw, it replaces the HD7790). I note, in the pane on the right, they recommend the 7750 as the best budget card. At a guess, the three cards are broadly comparable, so, depending on your budget, I'd go for the newest.
Surface Pro 5 News - release date, UK price, features, specs