I don't consider my 3130 to be too heavy for yard mowing, assuming the ground is relatively dry and you have at least R4's, and use 2wd whereever possible. I think any Grand-L series will leave significant impressions or ruts if the ground is wet, just from their sheer weight. I have R1 tires, so I don't do finish mowing (I have a riding lawn mower), but I drive across my yard all the time when the ground is dry. As long as I am careful about how I drive, I don't do any real damage to the yard (the grass pops back up in couple of days).
I do not know anyone with a tractor of the Grand-L size with turf tires, but most people don't seem to have any problems with yard work using R4s, as long as they are somewhat careful.
For your dual purpose mode, I would definitely check out a 3130 with R4s. They are intended to be a good middle ground between turfs and ags. I think you would find the turf tires lacking in traction when working on the 'unforgiving' terrain you speak of.
Even though it is 'smallest' of the Grand-L line, I have never had a complaint about the power of my 3130. I even made the mistake of buying it with the LA513 loader, but it still performs well for my needs. I can lift over 1,000 lbs with it no problem. I would recommend going with the 723 loader if you can afford it because of the four point linkage on the bucket (greater range of motion) and of course the higher capacities.