Otter, I just had one put together for the exact purposes you're considering and settled on 22".
Cool. Any pics of it?
Otter,
Rio has a good point on the .243 - particularly with dies, brass and bullets already in hand.
OTOH, I have .243 dies, brass, bullets and a rifle so chambered (also 22") with a 1:8 twist and I still cobbled together a 6 Creedmoor.
It's somewhere in between Vermont and my place right now so this is the best I can do for an image. 1:8 #3 Bartlein @ 22" in a hefty Grayboe Terrain stock.