Any rifle I buy, realistically I'll have to order it in from the continent which is a pain in the but.
So you're losing what like 44 odd fps from 24"to 20". I don't think the deer will notice anything
This should give you an indication:
.308 Win Barrel Cut-Down Test: Velocity vs. Barrel Length « Daily Bulletin
This is for the 308. For the 270, which you are also considering, the drop-off will most likely be higher.
So you're losing what like 44 odd fps from 24"to 20". I don't think the deer will notice anything