Well, don't know about everybody else but MO is usually what I buy for most of my base malt. I think it has a better overall flavour than regualr 2-row. Only occasionally will I substitute 2-row, usually when I run out of MO and I want to brew something before I can buy another bag of the MO. I've brewed pale ales, APA's, ESB's, stouts, and brown's. It does cost a bit more tho.
You should just take a few grains and chew them up, then do the same with your usual base. This can give you an idea of the differences in the flavour. I don't think you would be dissapointed or wasteful at all with the 25 % or even more in your stout.