While I have had good luck with the 3M belts, I have better luck with the Klingspor belts. If I am using pine I buy the cheapest belts possible because of the pitch loading in the belts(One just goes though them faster) but on oak I buy a little better belt. If you are a business you can easy get a business account and save a bundle. Have never been able to buy the 3M belt at wholesale prices. We do have the same sander as you.
Brice