"Do any of you guys measure case capacity"
I did, at one time. Don't now and haven't for maybe 30 years.
"and what is your thought on how this really affects pressure/accuracy"
Not much.
Yeah, sure it does affect pressure, some, and that MAY affect accuracy, at least a little. It will affect safety IF your load is already smoking an occasional primer pocket. Actually, IMHO, it's mostly anal agonizing over what's largely trivial. After all, while capacities do vary a bit, it's NOT a massive difference as some make it sound. Case differences are NOT going to blow up anything if the load is a safe one to start with.
Accuracy? Test it yourself. Accuracy is found within a range of powder charges that may wlll be .5 gr. or more wide, not a specific point, +/- nothing. Use carefully matched cases and load five in the middle of your loads best range, then load another five with the same charge but using cases with differenct head stamps. Shoot them iwth equal care.
You will then see how much difference normal case variations make to YOU! It may be as much as 10%, or even less. If so, your hoped for 3/4" groups (.75") become .825" groups; worse by a shade over 1/16th inch? And, since that must be split in half as the decrease in accuracy from the point of aim. it becomes about 1/32th inch worse. Whould that make the time measuring case capacity worthwhile? Not to me!
A 10% improvement, or whatever small amout you may find, difference mean nothing to a deer or ground hog and precious few crows. And, of course, it makes some difference in any competition shooting, especially long range.
I do segregate (most) of my ammo by brand and keep track of how many times it's been reloaded. And that's it, these days. (I learn slow but I do learn!)