A fast twist 243 will do anything a 25-06 will do on big game. It shoots similar bullet weights (107 vs 110) about 150 fps slower. Or a bullet weight 10 gr lighter (107 vs 117) to about the same speed. At the muzzle the 25-06 has an advantage on paper, but at about the 250-300 yard mark the higher BC 243 bullets catch up. Your 22-250 is a better varmint rifle, your 30-06 the better big game rifle so I don't see a use for either 243 or 25-06.
The 7-08 is a ballistic twin to 308. At 500 yards with the best loads in each the 7-08 has just over 2" less drop and less than 50 ft lbs energy advantage with 1 ft lb less recoil. On paper the 7-08 has the edge. But not by much. I could live with a 7-08 or 308, but other than being in a lighter, more compact rifle you don't gain much over the 30-06 you have.
Either of the 6.5's will beat 25-06 on big game, does 95% of what 7-08 does and fills the gap perfectly between 22 and 30 caliber. With lighter bullets it could be used for varmints, but with 140 gr or heavier bullets it'll kill anything 270 or 7-08 will kill and do it with almost 1/2 the recoil you are getting from your 30-06. If you want to go long range target shooting the better high BC bullets will get you way out there. Of course a 243 could too.
If you want nostalgic, buy a 6.5X55
But from a practical standpoint there is a good reason the 6.5 Creedmoor has taken off. Lots of good, accurate, reasonably priced rifles out there and ammo is available. It comes close to 308, 30-06, 270, and 243 in availability and price. Much easier to find than 7-08 ammo and 6.5X55.
