I recall seeing a post from the CM vendor explaining the differences between the two models, but I do not recall what the differences might be. I have a CM QFS with Cherry mx greens, and it seems like a very solid board. The only issues I have with it are that I do not particularly like the font on the side-printed keycaps, the braided USB cable is too stiff, and the recessed area on the case for the mini-USB connection is too small for easy connection and disconnection of the cable. You might be able to find more about the differences between the two models on the CM site.
I am not sure about modding the position of the mini-USB connector, but in principle, it ought to be possible.
Regarding rubberizing the feet, I have used two methods. One is to use self-adhesive rubber strips, which you can get at the hardware store. Another is to cut some rubber or silicone-rubber tubing into small pieces just a bit narrower than the feet, make a longitudinal slit in the tubing, and slide the slitted tubing onto the feet. Find some tubing at the hardware store that is thick enough (small enough inside diameter) to fit snugly onto the feet. I prefer the tubing method, and I have used this on two of my keyboards; it works well.