I agree, 22 won't hold you back. I've gone as long as 26" on my large frame and while it wasn't bad moving around barricades, it did feel quite awkward. 22" is a happy place for both my 6.5 and 6mm creedmoor's. I plan to stick to that with the valkyrie and with the lower powder capacity that it has I doubt I'd be losing much velocity to a longer barrel.
FWIW, the deference between my 18 & 20" grendel is around 25-30fps... my 16 vs 18 is almost 100fps. Comparing 223 is very similar, but more loss between 16 & 18"... though I only have but one 16" vs 2 18's and one 20.
My swag... I'd say the valkyrie will peak around 20-22" with longer barrels being marginally faster while using heavy bullets and extruded powder.