yep, still the same 24mm=24mm. It doesn't matter if the lens is built for APS-C or 35mm (full frame), it is still the same focal lenght. Field of view changes from APS-C to 35mm because of the 1.6 crop, but that doesn't change the focal length. I think where the confusion has set in is where it is believed that a lens built for a crop sensor has a true field of view at the given focal length when in actuality you still need to multiply the focal length times the crop factor to get the field of view.
All focal lengths for each lens are based on the 35mm equivalent, therefore it won't matter if the lens is a crop lens or a 35mm lens, they focal length printed on it based on the 35mm format since it is the standard for measuring focal lengths. Since some lenses are built for an APS-C size frame, then that means that have a narrower field of view which would cause vignetting on a 35mm (full frame) format.
Again, the OP would get a wider field of view using the 17-50 lens vs the 24-70. He would be missing the 7mm on the wide end if he uses the 24-70, but the OP also stated that he would rather gain the extra 20mm on the long end. I have the 24-70 and I love it. I am sure there are limitations for some being that it isn't a true 24mm FOV on the wide end, but it suits me just fine.
EDIT: Sorry, it seems there were other posts while I was writing this to clarify the issue.