Nice choice of soaps to rotate between. I use all three (Windsor version of D.R. Harris). Note that D.R. Harris has two base formulas, one with tallow first and another (used for Windsor) with tallow second. I also use Cyril R. Salter's shaving soap that uses the D.R. Harris tallow first base and find it lathers a bit easier though both are good.I received my first puck of D.R. Harris and have used it for three shaves thus far. It is a hard, dense soap. My guess is it will last a long while. As for the performance, so far it is very good. Lathers well and provides a slick cushion. I am going to have to rotate Williams, Mitchells and D.R. Harris to see how they compare. I use Williams on a regular basis and have done for years but since it is not being made anymore and Mitchells has gone tallow free, D.R. Harris may well be my best replacement choice.
I've also stocked up on my favorite tallow soaps with plenty of back ups for Williams, MWF, Arko and Cyril R. Salter. Also have a few non-tallow Razorock What-the-Puck soaps as they work well and will have a long shelf live since they are triple milled. Currently rotate between all of these and a few others including some custom blends.