Have a couple of 303-25's - one on a No1 MkIII action and the other a P14 action. Really like the cartridge as it was my first 'quarterbore' and it worked perfectly on everything from rabbits to large boars. I loaded 100gn Taipan HPs over a mild charge of AR2206. No sense in pushing the SMLE action too hard and besides, the 100gn load was able to print 5rd groups of about 1.5" in the old action.
Then along came the P14 and as it's a front locking action I could push the case with 90gn BT pills over AR2206H. This rifle produced sun-MOA groups without too much trouble.
As for the 25-06, also a great cartridge but one that I'm not looking to add to the safe as I have it covered by a 257Rob Ackley Improved and a 257Weatherby Magnum.
From my perspective I'd use a 100gn load for the 303-25 and work up a flat shooting 85-90gn BT load for the 25-06. This will give you the coverage of everything up and including red deer/donkey etc, out to 350-400M.
You've got two great 'quarterbores ' there - one a piece of Australian history and the other a great flat country round.