I'm interested to know the results of your testing since I am in the same position as you.
GTX 680 MSI Lightning and considering another card.
Surely your card is already good enough to play bf4 on ultra :O
Please remember that any mention of competitors, hinting at competitors or offering to provide details of competitors will result in an account suspension. The full rules can be found under the 'Terms and Rules' link in the bottom right corner of your screen. Just don't mention competitors in any way, shape or form and you'll be OK.