That's all the info I received on the matter. Sounds like it's a minor thing but interferes slightly with the adaptive resolution feature. I wouldn't expect huge performance gains in games like Zelda or anything.
The bolded is probably thread worthy itself
From what we understand, there is a small issue with the current firmware on Switch which causes a slight drain on GPU resources - once corrected, we're told that Fast RMX should sustain a full 1080p in docked mode.