Here is my experience on my Vulcan 500:
Original Bridgestones--8K miles front and rear
Dunlop 404 (two sets)--front 10K/rear 8K for each set
Running ME-880s now and the front has 8K on it and it still has plenty of tread. The rear has 3K miles on it and it still looks new.
I replace mine before they get too slick; 1-2mm range.
2006 Vulcan 500
Saddlemen Cruis'n Large Slant Saddlebags
Kuryakyan Foot Peg Extenders and Pegs
Kuryakyan Iso-Grips and Throttle Boss
Memphis Shades Alley Cat Windshield
Kawasaki Luggage Rack