Bit of an update - had to fit a new front tyre on Friday last week. A bit disappointed with the life, I must admit I can't remember exactly what the mileage was when it went on, but I do a fairly reliable 12000 miles a year, and it was fitted as one of a pair last October. So definitely less life from an R5 front that the previous two pairs of PR4s that were on there, all of which survived a full year and wore out both together.
The rear, however, still has a fair bit of life in it. It's clearly not looking new any more but I reckon there's at least 3k of life left in it with my riding pattern, so I only changed the front.
Grip was still fine and it didn't move around on bumps, banding etc in the road, whereas the PR4s were quite bad for that when they got worn. However on the right-hand-side of the tyre, which gets more wear because of roundabouts, it was right down to the wear markers in the tread. I didn't fancy risking a heavy fine and 3pts, so I got a new one, another R5.