Up to you, but I think this is a good target. I believe you should be able to shave a whole week with one blade, no matter what the manufacturer. But I agree with OP that going lesser number of shaves, say only 3 will provide optimal performance every single shave. But you should be able to go twice that number (6-7) if you pay attention to technique and still get good results.
This is completely YMMV based on your face and your blade. I use Feathers and have a heavy beard; my blades are done after 3 shaves. I would say use three or four as a baseline and then just monitor your results, you'll figure out an ideal blade life pretty quickly.