7 days with my Voskhod blades. On a side note: I think I have more nasty used blades in my bank from the people who sell an item on eBay with the original unwrapped vintage blades than I have used myself over the years.
DE blades can vary but. Do 3 using regular DE and able to get 2 more thereafter using the slants. Injector Blades 7-8 Gem 3 at best (I know wire whiskers)
Mine range from 3 on Voskhod to 12 on Derby to an extreme of 21 on GSB. 5-7 would be normal, so I guess I am about like you.
Full disclosure, I have only used three Feather blades lifetime... Day one and day two were very different from one another. Day three was a lot like day two. Day 4 stunk. What's you're experience with that?
I did this too when I first started. The "how long does a DE blade last" games I've played since are fool's errands really. The additional savings decreases each day. Besides, one could use a new blade for every pass and still spend less than some carts.
Yep it's so much cheaper I have changed my technique to 3 shaves and out with a blade. Was saving so much money vs. Dollar Shave Club and wasn't getting fantastic shaves the 5th shave so decided to do 3 instead.
DE makes perfected luxury affordable, if one so desires. My generally reccomendation to new converts is two and out so that the edge stays consistent. If you venture into injectors, and a Schick E or G or J is something you really should try, the Chinese Schicks are made of thick stainless steel, and 10 shaves is common, making them reasonable at $1 per blade.