Thanks Hazmat and IslandTractor for your responses. They all make me think hard about this decision and in many cases re-justify my current thinking.
Yes I have a medium sized utility tractor, a Kubota M7040 rated at 68hp. My previous tractor was an M5030DT of similar size. I went with the 7040 for it's size/weight (and I'll admit it - the cab) and to be able to use all my current implements.
My expected grapple uses are as different as the next person. My highest need is to get some help out on my trails popping rocks and stumps, next is doing the same in my fields, next is moving logs around, and my lowest need is handling brush piles, which I do about one month a year.
I don't expect to pop every rock or stump I come across. Right now with my old backhoe that is being traded in with the old tractor (that's another story for another thread), I get about 2 out of 3 that I try, and I bury the stubborn one til I can hire an excavator. I don't even expect the grapple to be as good at this as the backhoe. But I do think I'll be able to do a wider range of tasks out on my trails when I have this grapple mounted, and I want my box blade on the rear most of the time.
Hazmat regarding your suggestion to get a bigger unit, I'll try to respond to getting bigger as in wider and then bigger as in heavier. My tractor could certainly handle a wider grapple, but I'm not sure I need it. My only use where width might help may be in log handling where it could provide more stability. But Island has already pointed out that anything 48" or more should be able to handle logs, and it all comes down to the operator and how they use the grapple. In fact with all my rock and stump popping, I'm also considering a dedicated narrow bucket/grapple just for this use. And when I think about all my uses, most of the time I want to deal with single objects - one rock, one stump, or one log. So precision is more important to me than the sheer grabbing size of the grapple.
Regarding your suggestion to get a bigger unit, as in a heavier duty one. I have considered this and have looked seriously at the Markham Extreme Gator Mini Rake. It's about 36" wide, 450 lbs, and uses 1/2" steel compared to 3/8" for many of the other light duty. At that narrower width it doesn't have a huge weight penalty for the move up to thicker steel. But I'm a little hesitant about a 36" wide grapple working with logs. This might be to narrow and force me to spend a lot more time being even more careful about finding the center point with my logs. And the challenge with alot of my logs is they are 10" on one end and 6" on the other, so you have to take an educated guess where the balance point is. But going with a more traditional heavy duty grapple, like Markham's 60" grapple rake at 770 lbs, pushes me way up there in weight and forces me to go with two arms. The two arms is the biggest negative for me because again I'm mostly dealing with one object and one arm will give me more precision and be easier to work with.
One other personal preference that again reflects my particular uses is that I'm looking at a 4-n-1 bucket, and if get one it will be narrower than my regular bucket. Most of the time when I'm working with my loader, I'm putting the material in my Polaris Ranger or a trailer towed behind it. My current 6' bucket is too wide and I spill a lot of material over the sides. Sometimes I do the corner bucket technique to pick out a half load, but when I'm dealing with heavy rocks I don't think that imbalance is good for my loader arms. So I'm looking at 5' wide 4-n-1s. I know this is slightly backwards and my tractor could handle a much wider one. For the 4-n-1's dozing function I also recognize that at 5' I won't cover my wheel stance, but my box blade does. So I'd use the 4-n-1 as a first pass dozer with a little less stress on the loader arms, and have my box blade do the second wider pass.
If you see anything wrong in my logic for my particular needs, please jump in and straighten me out. I really appreciate everyone's input.
Thanks, Mike