Best not to waste a RR on perp down, but rather instead, use RR for a strong build of avatar attack/accuracy or magic attack/accuracy then macro it in for those pacts. After pact use, then swap back to this, YY, or AF2, whichever you got.
As much as I like perp cost down, you'd be doing yourself a dis-service for not boosting avatar with a customizable body piece while can.
Penance robe is actually an excellent body piece if you have multiple jobs and have to partake in endgame, personally I never get to come summoner to any events so MW was better suited to my needs. I'm a proud owner of a penance robe, it definitely turns heads.
What Tukeuke says is partly right.
Penance Robe is pricey AND rare, where Royal Redingote is more or less free. If youre serious about a full perptuation set, but dont have 5~6 millions laying around Use a RR. If you do have the money and know where to get one, sure go for it.
TBH i wouldnt waste RR on something like Prep -2 i would rather keep my YYR and make RR with Pet+ stuff like ( Crit hit% and Double Atk or Atk +15) for BP macro onry ofc but thats just me idk about you other Smn but i'd rather have an uber dmg predator claws over -1 more prep
AF2 Body: -3 Avatar cost on avatar's day (Darkday = -3 Fenrir, Earth -3 titan, etc)
This with AF2 is uber... And only took my *** ~15 synths. Best part, on Midgardsormr, the NQ is either break even or profit- usually profit and sells fairly decent. If anything, I MADE Gil on all 15 shots in a half year span and suffered 2 or 3 breaks while at it.