Building new, I'd probably put the HD7750 at the minimum end-point, especially if size is a concern (there are low-profile versions), and the intent doesn't include the latest games on "gorgeous" settings. Older games, and even newer ones on lowered settings will run well on this card (remember how graphics cards used to struggle with Oblivion...) With no size or power constraints, a HD7770 or GTX650Ti is still a decent card, able to play any game, and ought to manage "sufferable" settings even for new titles.
There are still a lot of people upgrading out there, who have older IGP's and/or limited OEM PSUs for whom the HD6670, HD6570, or even (for Blu-Ray) HD6450 remains a valid upgrade.