Re: short action or long action for 22-250?
I would go with a short action.
When you say a heavier bullet, do you know what you want to shoot?
If you are thinking 75/80 gr Amax go 8 twist.
You may have to give up some of the lightly constructed lighter weight bullets at max velocity (stuff like the Hornady SX) with the faster twist.
If you are looking for a slight step up, the Hornady 53 gr Vmax has a good BC for its weight class and a 12 twist should work nicely and still let the other lightweights run full speed without flying apart.
I'm not a fan of fast twist, light jackets, high speed and 3 groove barrels.