The two bikes are closer in weight and power than you might think. I'm not sure if these specs are 100% accurate, but here's a comparison:
2012 V-Strom 650: 65 peak HP, 485 lbs wet.
1983 CX650: 65 peak HP, 480 lbs wet.
I'm not saying that the CX is the equal of the Strom (the Strom will DEFINITELY out-brake the CX, and the frame is stiffer, and the electrics are better, and a bunch of other things), but it does seem to be in the same league, at least on paper.
I got those specs from these sites: