Huh? This is illogical. Besides, the 560 offered better performance per dollar than the 560 Ti when it launched.Nvidia won't waste the chance to milk the 660 name for all it's worth.
If there are two different chips, the faster 660 Ti will be GK104 and the slower 660 will be GK106, with 660 SE for the salvage part of the GK106. This let's them ride on the success of the 660 Ti being faster than the 7870, while the actual 660 (GK106) is slower but almost certainly more expensive. I'd put money on this.
They did this with the 560, they'll do it here. If Nvidia excels at anything it's confusing their buyers and they'll lap up the slower 660 based on the prowess of the 660 Ti.