Well I Recently Bought A 6750, Only Beacuse The 5750 & 5770 Was Out Of Stock!
And Yes The Only Major Difference Between The Two Is That 6750 Has HDMI 1.4a!
No Difference In Gaming At All!
Its Basicaly The Same Hardware, Rebranded With Some Very Minor Changes! If You Can Get The 5750, Then Go For It!
PS: If You Can Really Edge Up Your Budget A Little, Get The 5770.. Its The Bang For The Bang In That Range!