I still have another 3 burned 7950 cards to send back, but they said that it would be ok to replace those too with R9 280.
The fact is that the HD 7950s fire up at a whopping 300 W against 220 W for the R9 280, while having a slightly higher hashrate. So I'm happy to exchange them.
But the problem is R9 280 cost cheaper then R9 280x. So they should do like partial refund or some free accessories..