IMHO, having used the 550ti both solo and in an SLI setup, unless you think THAT's defective you could probably put off upgrading the 560ti. I originally had a 1st gen Intel i7 chip and got decent performance out of it about three and a half years later but upgraded for the same reason you are. Most of the problems I could lay on an underpowered system...
With an i7-3770k that's been overclocked to 4 Ghz and a GTX 660 I'm running FFXIV at the highest settings I can at 1920 x 1080. Aside from some shadows acting a wee bit odd when the sun was setting, I've had zero problems, and been easily getting between 40-60 frames a second if not more. Anything in the Core 2 range? Your CPU is definitely your bottleneck.
With an i7-3770k that's been overclocked to 4 Ghz and a GTX 660 I'm running FFXIV at the highest settings I can at 1920 x 1080. Aside from some shadows acting a wee bit odd when the sun was setting, I've had zero problems, and been easily getting between 40-60 frames a second if not more. Anything in the Core 2 range? Your CPU is definitely your bottleneck.