Well, I took TripleR's advice and rented a bucket - which was a good reminder of the many other specialty SS attachments I could rent for specific jobs but never justify buying (eg. A rock bucket).
I dug out a 10' X 22' area by 4" at one end and 15" at the other. It had grass on top, with loam, clay and a few gravel spots (probably part of an old parking spot). A few rocks but nothing major and no big roots. There was 8" of snow cover, so it was a bit wet but not muddy. I have a Kubota
L3540, Ag R1 tires and no wheel ballast or weights - just my snowblower on the back for FEL ballast. I ran it in 4WD.
I used my 72" Kubota materials bucket and my rented 60" toothed, low profile skid-steer bucket. Observations:
1. The tooth bucket is definitely heavier but I could still fill it with loam/clay and lift/curl without any issues.
2. The tractor worked less to push the tooth bucket into the dirt, it was fairly smooth operations.
3. With the materials bucket, I had to use the diff lock quite often, never touched it with the toothed bucket.
4. With the bucket dumped to the limit, the toothed bucket was not as vertical as the materials bucket, but it never caused an issue.
5. The tooth bucket always managed to dig in and lift out, the loss of break-out was not a factor in this job (albeit it was not a large job).
6. I got a nice straight edge on my area with the toothed bucket as it was easy to control, due to above traction/tougher work the materials bucket was not as good, it would want to wander a bit instead of a straight line due to resistance or traction issues.
7. The finished grade on the area was pretty flat with the toothed bucket.
I did manage to exceed my loader limit with the toothed bucket when I pushed into a gravel pile right to the back of the bucket - couldn't curl or lift. Did the same with the materials bucket and it lifted right out of the pile. This is where the bucket weight and cutting edge distance was a factor. But that would be loader work not digging!
The job took about 90 minutes ( including hauling all the dirt about 300 yards away). It would have been faster with a skid-steer but not once I add in travel and paperwork time to rent one. While the FEL is not a digging/excavating machine, as a homeowner with a CUT for many purposes, it was a good compromise for such a job.
Overall, the skid-steer toothed bucket definitely improved the digging performance of my tractor without seeming to give up anything.
I liked the suggestions of using a 3PH implement to rip up the area being dug - I will add that to the repertoire, it should simplify and speed up many jobs.
As for a tooth bar, the price I was quoted by my dealer was $700, which is why I said "for that I could buy a used tooth bucket and have money left over" - hence my quest.
Thanks for all of the advice and experiences.