Sapphire make among the better AMD cards, quality wise, performance wise and price wise. The 270x is, imho, the top AMD card in the mid-range class. It bumps heads constantly with the GTX 760. The 280 is, imho, the lowest AMD card in the enthusiast class of gpu's, and is right behind the GTX 770 in performance. The 280x bumps heads with the GTX 770. Any way you want to look at it, any of the enthusiast class gpus will outperform the mid range class, and by a pretty wide margin. Explains the need for the more powerful PSUs.
Yes, I'd wait and get the Sapphire 280.