I have used Ultimox 226, Krytox 224 and Krytox 223 and they all work well and no detonation or dieseling. These all have a anti
corrosion additive, but the 205 will work just as good. as said above strip all old grease off and out of everything, even then usually the first time it’s used it will still find and leech out the old grease, you’ll know this because it will turn the white Krytox grease dark. Over time when the rifle is taken apart and cleaned out again it will stay white once all the old lubes have been completely Stripped away.
Krytox works in cold and heat and it stays on the metal parts requiring a special remover to completely strip it off of the metal (according to dupont website) I would think brake cleaner would work though. It only requires a really thin coating, no need to glob it on everything.
If your spring is twangy then you need a tighter fitting guide, not globed on grease or tar.