Based on a pal's experience, mono 350AR's would be the way to go. The improvement was sufficient to have him call gushing, "the 350 was great but as monos the difference is amazing!." I can't add any personal comment as I wasn't able to get over for a visit during the brief reign of that set-up. Shortly thereafter, he jumped to the Belles class A monoblocks. He's now running them with Dave's new linestage, switching from the 28A.
Neither of us has ever heard mono 150AR's, so can't comment. But, yes, Belles says the hierarchy is 150AR,350AR, 150AR monos then 350AR monos. BTW, even my solo 150AR makes fabulous music; Dave's creations are the real deal.