this has been a great discussion here lately. I used to target a room temp mash PH5.2 for pils, wit, etc and 5.4-5.5 for IPA and darker roast beers. most recently, after reading some opinions on this, I started targeting a room temp mash PH in the 5.3-5.5 range for everything...referenced by some as a nice blend for optimal room temp mash PH. I then adjust after mash up or down- pils 5.1-5.2 and porter or other dark beer at 5.5-5.6 into the kettle.