Witness,

The action will work fine with the 250/3000, go for it. Long is not a problem, too short is. You can install a block at the back to reduce the distance. I am glad that Gander Mntn treated you well.

The 6mm Rem is one of those great "might have beens" except for the dumbs**t marketing department at Big Greed. Instead of selling it as a combination deer/varmint gun they decided that it was a pure varminter. Even though it is technically a superior cartidge to the .243 Win., it was unable to compete and fell by the wayside. Possibilities? 1. Bore it out another .5mm and make a classic European 6.5x57. Outstanding cartridge!
2. Bore it out to .257 and make a Roberts out of her. Not much better for light NA game.
3. Work up some loads with both 60 and 100 gr. bullets and have a better combination gun than the .250/300 would ever be.

Personally, I like option 1 but a more sensible person would probably go with 2 and a hunter (not to be confused with a gun nut) would take 3.

If it was me - and someday I hope it is - I am thinking a nice 7x57mm - classic simply classic.