I do P,R,M,I for thrash metal if needed. The only thing that's difficult is maintaining the callous on your pinky as it doesn't get used otherwise! Wish I could do that Matt garisson technique you describe, maybe I'll revisit this?!
PRMI for me. But I rarely use the four finger technique, in most cases where I would need to use it, a pick will also sound better and more consistent, so I use a pick instead. The only situations where I actually use all four fingers are when I am noodling on a 6 string, classical guitar style.
I do some Flamenco style chording, with thumb on bass notes, and fingers strumming the upper notes, and I do it T R M I.
TIMR. It took me a few weeks to get comfortable doing it (as RMIT feels more natural), but I feel TIMR gives more of a consistent rhythm (ie, less of a gallop).
