Couple comments:
-- Once brass is fired once or twice in a given gun, the outside dimensions of the cases are pretty much identical unless you are resizing full length and bumping the shoulder back to factory. Which you shouldn't be doing.... If the outside dimensions are the same, and the brass has different weights, then the inside dimension has GOT to be less for a heavier case. Period. This is a basic law of physics. X amount of brass occupies x/130 space in CC.
-- However, brass is a LOT denser than powder. Right at 130 grains/cc. H4831 is 14grains/cc So brass is right at 9x denser. So for instance, a case that is .02 grains heavier, can accommodate .002222 less H4831 in terms of volume. Meaningless. I sort cases into lots around 1 grain of each other. That amounts to a very negligible variation in internal capacity.
-- Back to you Hornady versus RP brass. 20 grains difference. That's actually quite a lot. 0.15 cc, or enough space to accommodate 2.15 grains of H4831. I would be VERY careful loading the heavy brass with the same load as the light brass.
-- Another way to look at it. A 257 Roberts has 57grains of water capacity. A 25-06 has about 65 grains H20 capacity. Filling a 257 Bob with a 25-06 load would be catastrophe, right? Well, a 25-06 case that weights 20 grains more, or 0.15 cc less internal space will have 2.25 grain less H20 capacity. It will be 28% of the way towards a 257 Roberts case capacity.
Weight of cartridges most certainly matters, but less than a lot of other things. It is VERY clear with your example why sorting by headstamp is a good idea at a minimum.
Finally, if you are interested, I have a large lot of various headstamp 25-06 brass. I think at least 40 rds of Hornady. Many more, in the 100's of RP and Winchester. I no longer own a 25-06. I am not alone. The 25-06 is declining in popularity. I and many others will sell you new 25-06 brass (much of mine is unfired) for a very reasonable price. I would pitch the 270 brass. Why lose 2.25 grains of case capacity? You are short changing you quarter bore...... Like my example shows, you have moved your 25-06 28% of the way to becoming a 257 Roberts.