Cans o' worms are a specialty here! LOL It sounds like you have ID'd a possible reason for the pressures to be a bit lower. Good that you are being proactive on this, IMO. Can't offer any insight on RP as I never have run it; but I can't find any published numbers on the ZDDP levels; supposedly the HPS versions have more ZDDP, per their advertising claims, but I don't know quantitively what that means.