Re: Splat factor?
Both will do exactly what you want them to do. Both have awsome range when used properly. and when set up correctly, with proper varmint specific bullets, can make a good splatter out of some tiny critters. Cost of ammo would be my biggest concern, and if that's not a problem then you really are in a win/win situation.
When you factor in the possibility of wind though, the 6mm's outshine the 22 calibers. I'd personally go with a 223AI(#1 choice) or a 243AI(#2 choice) and be done with it. Another thing to consider is that i get the feeling your just threading up a new barrel for an existing rifle, if that's the case then take into consideration what boltface you currently have.
I do have to admit though, my 300WSM with 110grn Hornady V-max's loaded at ~3700FPS sure does a number on the yotes...