I am the exact opposite, I wouldn't take a set of Diablos for free. Tried them, got 2400 miles out of the rear & cord exposed. They took longer to heat up than the PP, & just didn't feel as stable in the corners as the Michelins. I run 2CT's & get 4500 out of a rear.
I would buy another PP rear then replace as a set.
You are absolutely correct! If you use your bike as a commuter and concerned about mileage, performance is secondary when choosing a tire.
My experience with the Diablo's was great for 1000 miles, they then fell off rapidly by 1800 they were done cord showing... and the last 500 miles I shouldnt have ridden with them, actually got sideways a few times. I never bought another set and wont. I dont commute on the bike but like the longer wear and they are plenty sticky at least 10x better than the stock slipstones that came with the bike.
Doyle I wouldnt mix these tires, especially the way you ride.
Also if you place the tires side x side you will notice the Pirelli's have a higher center than the pp and they tip in a lil quicker. So if you mount the Diablo's do both and get ready to order a new PP soon.
my six cents