Brass lots with different case capacities (H2O)

[sandman]

Okay, so I recently got back to reloading for my 7mm-08 and I need to make a change. I had been using Federal Nickel cases (case capacity 53.5 grains) but my brass lot is near it's end. After 5 firings, I've started to see a few split necks, so it's probably time to pitch the whole lot. No complaints as I've gotten plenty of use out of these 100 cases.

I just bought 500 Hornady match 308 cases for a steal, and have full length sized 100 for the 7-08. I built a dummy round to ensure it chambers, given what Rocky, et al have recommended about the increase in neck thickness. It chambers with no problem. Good so far.

Case capacity of the new cases is 55.5 grains of h2o.

Is it safe to assume that my current petloads (under book max with no signs of pressure in my rifle) would be safe in the new brass?

Also, can someone clarify a question I have about pressure. Does the size (capacity) of a given case impact the pressure generated? I know I could fit more propellant in a larger case, but if the powder charge and projectile are kept constant would the pressure produced be equal between the two cases? Is the 3-4% increase in case capacity that significant?

Sorry this is long and maybe I'm overthinking it. I am going to back off a couple grains and work back up, but I was curious to know what the gurus think.

Also, do you guys have any reliable (preferably permanent) way to mark the brass that now sports an incorrect headstamp? Unfortunately I also load for 308. I may just keep this whole lot of Hornady brass for the 7-08 to keep it simple.

--
Steve