Looks like you're about at the same point I am in the shopping process. Speaking only as a determined shopper, here's what I've been able to figure out so far.
Outfits like Woods, Bush Hog, Bradco, etc. make good products that are very comparable to the Kubota backhoes.
The large Kubota hoe, the BH90, is a new model and compares very favorably vs. the competition. You might save a little going with one of the non-factory models, but on the other hand, your Kubota dealer will stand behind his products installed on your tractor. Many Kub dealers also sell one of the other brands, and may work a deal for you.
The BH90 is a lot more hoe than the 4690 for about $1000 more. If you expect a lot of heavy use (i.e. commercial), the BH90 would get the nod. If you are more in the amateur category like me, the 4690 should be adequate. Your 3130 should handle either one or one of the other brands with no problems.
I hope maybe some of this helps. /forums/images/graemlins/laugh.gif Good luck.