I don't think the plate thickness is relevant except to have enough engaged thread length to get the devices fastened down adequately. What I think is important for best heat transfer is the flatness of both the plate AND the original heatsink. I file & then lap my heatsink plates with compound on a piece of glass. My 780's heatsink was not perfectly flat when I put a straight edge across it. The 780 heatsink is a flat piece bent into a 'U' shape. The mounting surface proximity to the bends and the pressure of the brake dies from the bending operation leaves it not perfectly flat. Mine had a tiny bit of a 'wow' to it. I can't recall if it was convex or concave- so I removed the heatsink and knocked the mounting surface down flat with a fine bastard file. Didn't take much. My buddy whom I made modules for did not do that with his and he has had no problems so it may not be enough to cause an issue. My suspicion is the original STK's will flex a minute amount and conform to the surface somewhat. Our 1/4" or 3/16" solid heatsink plates will NOT flex under the light tension of those two mounting screws. I originally noticed it when my very thin layer of heatsink compound did not squish out evenly around the edges of the plate when I first bolted the plates down. After my attention to the heatsink, it did squish out evenly. Going too far? maybe. I tend to get a little OC about small details like that- but I rarely have to re-lick the same calf.