The R7 250X is a rebranded HD 7700 Ghz Edition, that's why it shows a different name, though both of them should show as the same unless one isn't, and that'd explain why it seems slower, so no the displayed name is meaningless. Take out one at a time and run Furmark for about 30 minutes, see if there's a problem.
You do need to think about replacing them though, the RX 580, which can FINALLY be found sub $200 on sale, is over 300% faster than the 7770GE/250X, and over twice as fast as two in Crossfire assuming perfect 100% scaling, which never happens.