roger, have you actually experimented with 2C-P? the belief that 2C-P has a steep dose-response curve gets passed around a lot due to the entry in PiHKAL. however, myself and many others that i have talked to have not noticed 2C-P to have a steeper dose response curve than most other 2C's (when comparing mg:mg of different doses). it is true that an increase of 1mg is more intense with 2C-P than with, say, 2C-E or 2C-I. however, this is because 2C-P is simply more potent.
i know this isn't a hard rule, but i'd say 1mg 2C-P = 2mg 2C-E = 3mg 2C-I or so. increasing your dosage by that amount (respectively) for each of those three drugs is enough to cause a fairly large increase in intensity of effect. ~1.3mg of 2C-P and ~2.7mg of 2C-I might be more accurate for that ratio, but of course it will vary in each person so whatevs.
anyway, to get on topic...
i'd imagine this combination to be pretty odd, but possibly rewarding. also i would imagine the effect to be fairly different than either compound on its own. if either drug alone is uncomfortable for you, this will of course be even more uncomfortable... at least through addition, possibly exponentially. if i had both compounds on hand at once, i would personally be willing to try the combination. catfish's idea of trying the 2C-I later into the experience strikes me as a good idea. 2C-P is both deeper and more subtle than 2C-I, so getting into that headspace first seems like a good idea.
I think one should only ingest this drug combination when approached with caution and prudence. Start with low doses and work your way up, and be patient.
these are wise words, btw.