W/r/t roller diameter: yes a larger roller* gives faster action and greater area (1928-84 H-D rollers: .855"), but there's a penalty.
When the valve closes and the pressure on the lobe is relaxed, the lash appears under the roller. When the opening ramp comes up again, the roller has to accelerate up to speed before it rotates on its axle. Until that point it's skidding across the lobe. A larger roller has far more inertia to overcome (much more than a simple comparison of diameters), which makes this worse. The obvious cure is thinner roller "wheels" (less metal toward the axle) but I'm sure that invites crushing with those 1,000 lb. springs X 1.9:1 rocker ratio = 1,900 lbs. on the lobe. Remember your math: the locus of points in common between 2 tangent convex shapes is a line with no thickness at all.

* be very careful here: a larger roller wheel will do bad things on an inverse (concave) flank designed for a specific smaller size, and even on a conventional (convex) lobe the speed increase is not linear but varies depending on where the roller makes contact.