The entire discussion has been based on long range hunting... Not benchrest, so I thought that is what we were talking about yet.
... and Braz, there is an important difference between KNOWN distance, and SET distance. Benchrest is the same distance every time you shoot, unless you change events. Otherwise, 100yd, 300yd, 600yd, 1000yd.
Distance is the same.
Target is the same.
Position is the same.
You get sighters before you fire for record.
There are a great many people running fixed 36x or 42x optics for benchrest with success. While there are people using FFP for benchrest... it brings absolutely nothing to the table over SFP. I know a couple guys running the march 5-40FFP in benchrest. They're quite pleased with it. Yet they say the same thing... there is no real point in having FFP. If mirage is too thick, you can dial back a SFP and dump some sighters into the berm. Problem solved. Most of the benchrest competitors I have talked with don't use the reticle for their holds, they use the target itself.