Just put a set on mine earlier this year. Seem to be doing great so far but I'm not sure I feel a lot of difference between them and my original stock Ranchos? Maybe just me. The differences are primarily the 5100 series are set up for lifted trucks and the 4600 for stock height, otherwise they use a lot of the same components.
I put a set of these on my truck at about 50k miles as my stock Rancho ones had been shot for a while. I immediately noticed a difference in the ride as it felt more like it did when it was new. I've read they rancho ones go out pretty quick.
I know when my Rancho's go out... it'll be Bilsteins for me. I remember when I put them on my 2K.. couldn't believe the difference in the ride & handling .. over the stock OEM's.
Installed the shocks today and wow what a difference. The ride is night and day. Can't believe how the oem shocks felt after only 4,600 miles. Manually pushing them down after removal I could actually feel dead spots in them. Truck rides like a half ton with them installed. Me like em.