The CL175 has so ever so very slight increases in some of the tube diameters. The backbone is a hair larger and a couple other tubes...by my measurements it seems to be around 1/10th inch or so on the backbone.
I'd be very curious to see a couple of stripped 160/CL frames weighed to find any hidden differences in beef.
I think my bike has a CL frame and Mary's a 160. Certainly haven't found any differences that you'd notice without a micrometer. Some of the tabs are a bit different. The rear brake cable setup on the 160 kicks ass compared to the stay rod setup on the CL. Just plain looks better and is easier to setup a rear brake pedal.