A couple of observations on a couple of the posts so far. Firstly, the OP was asking about +P, but the ammo he mentions is +P+. This ammo is even hotter than normal +P, and in fact there is no SAAMI spec for +P+. You kind of have to trust that any ammo labeled +P+ is safe in your weapon. Probably not too big of a risk with Winchester production, but something to consider.
Secondly, military ammo--including WWII German stuff is loaded to higher pressures than SAAMI spec for standard pressure ammo, and is +P as far as SAAMI is concerned.
To address the original question, if my weapon is safe to use with +P ammo, I'd buy a box or two of the +P+ stuff that was mentioned and see how my weapon shoots with it. If it likes it (ie, it's 100% reliable and nicely accurate), then I wouldn't hesitate to buy large quanties. I probably wouldn't shoot it regularly at the range though--I'd go with standard pressure stuff to reduce wear and tear on my weapon.