Should not be a problem at all the 750tx Corsair PSU is a good one to have. You should have no issues at all.
** Edit ** Just realized that you were asking if a 2gb version would run instead of a 1 gb version? Either will work fine. I thought you might've been talking about running 2 x 2gb's 560 Ti's (SLI), which the Corsair 750tx would handle them just fine too. Either way your covered