I have been doing this for many years with my E254 Colgan's set. I am always buying collections (large and small) of these and always check my new ones against my old ones and keep the best one for myself. Some cards have been switched out 5-6 times. It is also this way that I have found some new "head size variations" as I am always checking to see if there are any slight changes between the cards. I think my set would grade pretty well at this point (on average) if I actually cared to ever do that. **Shameless plug alert** I still need 30 for the master set so if anyone has some I need let me know.
-Rhett
Colgan's set:
http://www.starsofthediamond.com/colgans.html