I have found a set of blades I really like. I am at 80-100hrs and still havent sharpened them (allthough they are about due). And I am not easy on them at all. Doing alot of construction around my new place and same at the old with living in a woods. Always running over rocks, sticks, dirt clods, dragging one edge into the ground running down the ditch, etc.
After the first season with these blades I took them off to sharpen, but didnt and put them back on as they were still sharp.
They are Gator Magnum blades with Fusion. Standard blades for my ZTR are 2.5" wide and 1/4" thick. The magnums are 3" x 5/16" thk. Fusion is a coating added to the underside of the cutting edge that is like a layer of sintered carbide. Its on the underside so as you sharpen, you dont grind it off. I was really amazed at how well they held up after mowing countless dirt clods and scalping after I had the pond dug.
And I too use a flap disc, but dont leave a blunt edge. If you maintain the 30 or whatever degree angle, they wont dull any quicker per-say. IE: if you sharpen to 1/32 and consider 1/16" as dull. Making them sharp wont result in dulling down to 1/16" quicker. But they will wear down to that 1/32" blunt edge quicker, but from there on, they would dull at the same rate as if you started there.