50C is fairly typical for the "standard" phase control option. It should be relatively steady with a slight increase at load. As for the algorithms of the various settings, apparently they no longer do anything. All setting on X99 Strix will result in using the standard phase profile. This appears to go back several BIOS versions at least (on the Strix) and it was a very clear line in time when this was applied to my X99-Pro. It is unclear if this is a bug, but after reading the very unhelpful responses from tech support and some general comments from other Asus employees about "us not understanding the settings", I wonder if it was deliberate. I can hop back and forth between BIOS 3402 and 3505 and re-create the issue each time. No change on 3701. You are likely stuck with the standard setting. You shouldn't need direct active cooling at 50C, but is likely the warmest component on the board anyway.