I have no experience with Pirelli tires, but I made the switch from GP4000IIs to GP5000s (both the tubeless and tubed variety) a couple of years ago and have been riding Long Island roads without a noticeable change in the frequency of flats, which is to say, almost never. If the GP5000s are slightly less puncture resistant than the older 4000IIs, I don't believe it is enough to make a real-world difference. Last year, I sliced a tubeless GP5000 open riding in Manhattan in the dark. It was one of those deals that no tire could survive and no amount of sealant could fix. Otherwise, my GP5000s have been trouble free. Since then I have been riding the tubed version of the GP5000 with TPU tubes. If you were happy with the 4000IIs, you will likely be happy with the 5000s.