I would not use a 5w anything oil in your 250 or mine. 10-30 at minimum. I also add a 1/2 jug of GM EOS at oil changes for the cam.
I agree with tlowe on the super light (fuel efficient) formulations. The base oils are to light for older engines. I find the writings of Chris Longhurst instructive:
Car Bibles. The article is a bit lengthy but worth ones time.
Highlights specific to older engines - avoid xx-30 in favor of yy-40 where y=10 or higher. Also avoid oils rated higher then CF because downward compatibility cannot be assumed as the CF testing regimes are no longer performed.
