I've heard both, and I'd take T50p over the P5 any day. I don't like the P5 at all to begin with, lol.
T50p boasts all-around better sound - bass, midrange, treble, and I've forgotten P5's soundstage. It wouldn't surprise me if T50p beats it at that as well. It needs a good deal of burn-in. T50p has an interesting coloration, "ephemeral" seems to be the way to put it. Not my cup of tea, I prefer HD25-1 II. Otherwise, T50p is a good headphone. I love T50p's look as well, my favorite in that aspect along with ESW9 and SR325is.