So I dropped my Aff spec for destro, but I still mostly go Demo on fights. I'm trying to figure out a good set of reforge priorities (in general) so that I don't have to reforge every time I switch (or try to gear two specs differently)
Seems like the general case for Demo is Crit = Mastery > Haste, and for typical single target destro its something like Haste = Crit >Mastery using GoSup. Both specs seem to favor crit but Im not sure what to do beyond that.
The guides in the stickies have good suggestions for reforging. You should be able to get a decent reforge that will compliment both specs, but be better overall for the spec you play most.