Charles,
I'm very new to all this, but have learned to rely on TBN searches and internet searches. You may want to check out Hayden's thread regarding his setup -- he was touting the Bradco backhoes. Here is the link
http://www.tractorbynet.com/forums/kubota-buying-pricing/111269-wow-now-thats-tractor.html.
Took me a bit, but I looked up your tractor and it appears to be highest end Boomer model available (man after my own heart!). You'd have to check out if your tractor is compatible with the BradCo stuff, but you might check out the BradCo 509/511 and 609/611. I'm attaching the spec sheets for both of those.
The quick specs on the Woods and BradCo are:
Digging depth: Woods - 9' 1", BC509/609 - 9' 8", BC511/611 - 11' 1"
Digging force: Woods - 5070 lbs, BC509/511 - 5676 lbs, BC609 - 5908 lbs, BC611 - 6167 lbs
Operating weight: Woods - ?, BC509 - 1425 lbs, BC511 - 1594 lbs, BC609 - 1702 lbs, BC611 - 1847 lbs
It appears that the BradCo stuff has a bit more capacity, but I think it is more pricey as well. I think Hayden mentioned that the BC511 setup was around $11,000, including mechanical thumb.
I may be trying to make the same decision as you are sometime soon, so let me know what you go with and how you like it. Best of luck with your decision!
Dave