Ron,
I use this spreadsheet as a guide. In fact, almost all my loader work is either horse manure or wood mulch for my bride's flower beds and I leave the HeavyHitch on. I figure I have just over 400 lbs back there with that set up...HeavyHitch (approx 30-35 lbs) + iMatch (65 lbs) + 8 suitcase weights at 42 lbs (336 lbs). Again, that works for me but everyone has different needs or requirements. When the occasion arises for us to move dirt, I do put on our BB (610 lbs). And as you said, that may not be enough. Which I understand and seldom fill or overfill my 53" bucket.
Doug