I have a complete set of R1 wheels and tires and R4 wheels and tires for my larger tractor and have had them for about 4 years now. I find that I use the R4's about 80% of the time and the R1's about 20% of the time. Only for heavy mud and snow do I use the R1's. The rest of the time the R4's do a better job for me since they don't do as much damage to the turf or cleat up the ground nearly as bad.
With a 1 yard bucket on my tractor I completely blew the side out of an R1 tire doing some heavy loader work. That's with the R1 aired up to about 5psi over it's limit (to try to avoid rim damage). Having both is nice, but if I had to pick only one design, hands down, it would be R4's for me. Heck, even with a lot of snow last winter and a lot of mud I didn't bother to put my R1's on. All 4 of them are loaded and I have to use a sling rig on my forklift to change them to prevent a perhaps fatal accident. I'm a reasonably big strong fella, but I don't really want to play catch with a 1300 pound rear tire. I'm afraid it would ruin my day.
But, like the original poster, I enjoy having the ability to switch back and forth when conditions create different circumstances. On my tractor, the biggest R4's I could find were about 6" shorter than my R1 tires (rears). Even with the R1's being loaded, I seem to have better stability with shorter and much wider tires. I always use the R4's when bush hogging corn stalks. I must grow iron corn. I can't tell you how many times I've had a simple corn stalk blow a good name brand R1 tire. And, no, they don't warranty that.