Wireless n router

Hi guys
Just wondering what the story is with dual wireless n routers...as in 5ghz and 2.4ghz...I read an article saying atheros had released a chip allowing the two bands to work together achieving transfer speeds of up to 600mbs...is there any routers than can do this? I thought the dlink dir-855 might but I emailed dlink and they told me it only works at 300mbs...because I was thinking of pairing one with the dlink dap-1522 but I would prefer something thats 600mbs!
All help appreciated