Actually, with a SAAMI chamber, a thicker neck is probably a good think. Measure the OD of a piece of fired brass, then measure the OD of a pice of 308 brass sized to 7mm08. The sized brass should be .003 smaller than the fired brass for optimal accuracy. But you won't be able to get it that close, the SAAMI chamber has quite a bit of space and the additional thickness of 308 brass is nowhere near enough. In my guns, anyway; Don't take my word for it, measure your own.
Actually, FWIW, I've never had a piece of 308 brass sized to 7mm08 that wasn't still well within spec for a 7mm08 brass anyway.