ProRunner 450 AW
34 x 29 x 50.5
Ryanair
40 x 20 x 55
Definitely pushing it a bit (the thickness of combined camera/laptop bags always cuts it fine). Using the usual confidence tricks you may get it passed, but you could have to do that six or more times on the trip (and I've seen people turned away by security for oversize at one airport after they'd checked in - Schoenefeld, by the way).
It's not so much a case of whether or not anyone else got through in the past, but what would you do if you were refused?
I've got through with oversized before (about the same size as the PR450), but I always had a plan on how I could ditch some internal padding from inside the bag and crunch it down to the right dimensions, and known exactly what I could pull out and put into hold luggage and where it was in the bag.