Then the 5D mk3 is what you want, and what I'd recommend. It seems you now know enough to know what you want. :-)
The 24-105L kit lens on full-frame will give you approximately the same depth of field at f/4 as the 17-55 f/2.8 lens gave you at f/2.8 on your crop camera (at the same framing). It will zoom a bit wider, and a bit further than the 17-55 did. The body gives you 3 stops noise gain, f/4 is a one stop light loss, so effectively you can compare it to two stops increase with the same depth of field. If you're only shooting JPG without post-processing, you may even see up to 4 stops low-light gain compared to the in-camera JPG's of the 60D because the in-camera noise processing was said to be imroved as well (effectively 3 stops including the slower lens).
Fast glass would give you a 2-stop low-light increase but it would strongly reduce depth of field.