Yeah the "xp" saws are the "pro" models. But I have to tell you, there is not a whole lot of difference at all. Granted, my 346xp does run a little stronger than my 350, I cannot really say it is a "better" saw. It has a metal crankcase, and a quick detach air filter cover, which is a time saver. But the 350 is also awesome. The biggest difference is that the 350 has a little more midrange grunt, whereas the 346 has to be wide open to perform well. But when the 346 is wide open, LOOK OUT!!
Hope that makes some sense.
Also, regardless of which saw you buy, if it has a spur sprocket, convert it to a rim sprocket system. It saves money and time . Most of the XP models should come that way, but I have a few buddies that bought 346's and they had spur sprockets on them.
Good luck!