Digic 5 means greater processing power. That applies to burst rate and stuff, and video capabilities, noise reduction... With bigger (higher resolution, higher ISO) images, more processing power is needed.
Sensor upgrades are what determine resulution (the amount of megapixels) and noise performance (how much noise at certain ISO levels, how much maximum ISO). Note though that in a 70D, it's highly unlikely that there will not be a sensor upgrade. The 550D and 600D, as well as the 60D, as well as the 7D, all share the exact same sensor. It's getting old and they will have to get a better sensor in the next model. It will have better noise performance than the previous model, period. However, how much better is still uncertain.
Question is, do you need the extra improvement enough to want to remain waiting without any upgrade, or is the 60D's ISO performance enough of an upgrade for you to want to buy it now? (For me, coming from a 350D, it was easy: I went and bought the 60D. Massive upgrade, well worth it.)