No because a GTX 670 is so much better than the 550Ti you have now, that you will be blown away by the difference anyway.
A decent upgrade path would be the 670 now or the 660 Ti if you want to go with that advice. Overclock the 965.
Upgrade your Motherboard and CPU once the price has settled on the Haswell launch and then look again at a GPU upgrade.
Whole thing should take about a year.