Anything above 1333 will be pointless unless you want to overclock. Personally, I would recommend an 8GB 1333 kit with tight timings.
Something like this would be great while still offering some overclocking headroom:
Newegg.com - G.SKILL Ripjaws Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model F3-10666CL7D-8GBRH
But you may want to go up to a 1600Mhz SKU just to protect yourself for Bulldozer:
Newegg.com - G.SKILL Ripjaws Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL9D-8GBRL