Had the T30 on the rear before the PR4, and i can honestly say the PR4 is far superior in the wet.
The T30 would have the occasional slide on white lines, etc, but the PR4 has not even budged an inch in any condition i've ridden in.
As for not mixing tyres, i've never had a matching pair in 30 years riding, believe whatever you want but that's at least four incorrect things you've been told now.
So what if a tyre has been stored for TWO years, it's high grade rubber, not a loaf of bread?
At the prices Oponeo sells for world wide there is no way they have stock that's two years old of a very popular tyre, it's just simply not true.
PR4 is 100% recommended by 195 users on Oponeo as well, can't really argue with those figures.