bearhunter,
the answer is: YEP. 25/06 necks right down to 6.5, W/O problem.
otoh, if it was my rifle, i'd been busily "picking up" FREE 30.06 brass at the range & necking that down.
(i think of Jack Benny as a spendthrift.- when i can get FREE brass, that's what i go with. = the last trip that i made to the local range, i picked up over 500 30.06 cases that were "just laying there, waiting to be scrounged".)
ONE reason that i'm so fond of the .35 Whelen, .375 Whelen Improved and .400Brown-Whelen Improved is that they are POWERHOUSES & CHEAP to shoot a LOT.
(my next project is a 30.06 Browning BAR, converted to a .400B-WI, with all the "recoil-reducing improvements" that i can think of, including muzzle-brake. - SHOULDER PROBLEMS!)
for example, the .400B-WI is the exact ballistic equivilent of the (well-regarded in Africa) .404 Jeffery & it can be formed from FREE/range pick-up 30.06 brass & loaded for about 55 cents each. - otoh, a box of 20soft-point or solids in .404Jeffery is 112.00 +S&H.