I've shot 1 F class match which was shot as 600 yards with reduced target size. But I don't have a real F class rifle, I shot my Savage 12 FV in .243 off a bipod. F-TR is limited to .223 and .308 by the way. Regular F class is pretty much run what you brung, almost anything goes.
A good entry gun would be the Savage F-TR for that class, and they have a F class model also.