Re: Barrel Length
I had a full-bull (no contour) Douglas "Air-Guaged", 24" bbl chambered in .300WM and it was a shooter (sold it long ago). However, i've since been advised that it was exceptional to acheive that level of accuracy (.2" with 190grn SGK, RL22, Fed 215 primers and Winchester brass).
Why are you choosing a 20" bbl?
In any event, if were to stick with the two choices you offer, i'd like to try a Shilen (one of their Premium Match Grade).
Otherwise, there a good handful of superb barrel makers to choose from that i would look to before your choices.