For mixed results, I recently stopped specifying “you do it but” and instead say “you do something but..” then I look at my options.
Am I misinterpreting this? It seems to me that “You do it, but reduced effect” basically means “you partially did it” or “you don’t quite do it.” Limited effect mentions that success is diminished/a significant obstacle remains; basically, 1 tick on a 2 tick clock for The Thing. I might be overthinking it, but I stopped saying it that way to avoid a disconnect with the language of the 4-5 results, and the fiction I am delivering when I choose reduced effect.
I guess it depends on how well the player’s action matches their ultimate goal. E.g., “I want to kill those guy before they kill me” –> partial success is still helpful because now fewer guys are trying to kill you, so it feels like a success. “I want to kill those guys before they ring the alarm” –> if even one guy lives and he rings the alarm, that would feel like a failure. For that kind of 4-5 result, I think your method of “you do it, and…” sound better.
Part of my GM tool kit is this product, which does much the same with ‘But’s’ and ‘And’s’
http://www.drivethrurpg.com/product/145426/CRGE-Conjectural-Roleplaying-GM-Emulator