You currently have 2 x 270x's in Crossfire? At this point in time save the money you would use to buy a new GPU and upgrade when your system can't handle the games you want to play. Any new GPU you would choose would not really boost your performance noticeably over what you have without a large expenditure ($600+ US (R9 280X crossfire) for even a small boost $900+ for a decent speed boost for the R9 290 in Crossfire which I would say is the minimum I would go for performance wise as an upgrade from the 270X crossfire).