I think it's fair to say that American troops probably could have pushed further into Germany itself, and Austria, before the Soviets, but Prague is a stretch, particularly given how large a prize it would be for either side to capture it first. The Soviets were well prepared since the beginning of 1945 to capture it; they merely needed to reduce Berlin first. The US and British, on the other hand, were in no position to even effectively breach the Rhine in number in early 1945, let alone make a dash for Prague. It would be hard to justify such an action as well; Berlin was the greater prize to the common man. Capturing Prague may have changed the Czech fate in the post-war period, but I don't see how the Americans could justify such an offensive.