Do you have some extra PSU power?

No -> 750ti

Yes -> 760 (or 770 ...or 760SLI)

Watch carefully your PSU, one form an old PC might not be enought and cause your systems instability.

Q9650 OC 4 ghz + 8gbs + 660 OC and the game runs perfectly. I was planning to change my rig before I tested the betas but now Im sure I wont change my rig until end of this year,mainly to be able to play at maximum to The Witcher 3 on february 2015,but thats another story. ESO is perfectly optimized.

Since many seem to have missed it, the op already bought a card.

So, unless you want the op to suffer buyers remorse, I doubt that any more gpu suggestions are necessary.

I have a gtx 780 and I am happy.