Never compare tire profiles of unmounted tire photos, only mounted tires!
Here's the Pirelli Diablo 150/70 ZR 18 mounted on the 18" BST front rim (left, and new) compared to the stock Metzler ME880 150/80 17 front tire on stock rim (right, and worn):
To reiterate, IMHO, this "rear" Pirelli is the perfect R3 front tire when used with the BST CF front wheel.