If what you're after is IQ, you won't notice the 5D being much of an upgrade from the 60D in ISO noise and sharpness, you'd have to get to the 5d Mark ii to notice an improvement. The 18 megapixel APS-C sensor performs as well as the 5Dc's sensor in most conditions, often better. The 60D has much lower high ISO noise in spite of being a crop, though the 5Dc has a bit more sharpness.
Full frame does not automatically mean better IQ, the 5Dc is a pretty old camera with a pretty old sensor. If what you're after is full frame DOF though, go for it.
I have a 5D and a 5D2.
I thought of replacing the 5D with the 60D as I wanted some of the upgraded features (including video) for my backup. So I bought the 60D.
I would be exaggerating if I said the difference was night and day but, suffice it to say, I returned the 60D. I am still happy with the 5D as my backup. It was not a hard decision at all. The 5D is an amazing camera. Still.
To each his own.

