The way I would answer that, you just have to try yourself. The idea is grain refinement, which improves relative toughness. With low alloy stuff like 5160, this can be accomplished by thermal cycling (or quenching several times...but that can cause other issues). Cycling doesn't work for the high alloy steels, as they get hardened, hence prequench. There are some images that Larrin and maybe others have shown that the prequench does refine grain structure somewhat in the higher alloy steels. There is an image online from a tech manual or Tool Steel book of a chart about D2, and it shows different prequench temperatures and their affect on the "fracture grain size", that it does refine the grain. I think, in that specific case, the chart showed the best prequench temp for D2 to be 1700°F. I think if you have the ability to do so, give it a shot. Do some testing and see if you get an improved toughness. The improvement may not be noticeable in real world use, but it just might be noticeable. "Pre-quenching" is a relatively new topic for myself, and haven't seen it discussed among makers much until recently.