A Nice Cup of Tea
Refugee
Pssst... here's a secret...In my first playthrough now i noticed the High rise of gamestage too. Zeds being walking dangerous EXP-Banks are ramping up way too fast for my taste.
You don't have to kill all the zombies. No, seriously.
Lots of people are talking about how you are "forced" to kill zombies to go up levels quickly. But what does killing zombies and going up levels actually get you? Yes, it unlocks some perks, but it also pushes up the Gamestage and makes the zombies harder.
If you take it easier and kill as few zombies as you can get away with, then you have more time to scavenge, trade, and loot and more time to build and repair before the Gamestage starts going through the roof. For any particular Gamestage you'll be more prepared and better equipped to deal with it.
Rushing levels to get the higher perks is counterproductive because you're making things harder on yourself by ramping up the Gamestage too quickly rather than making things easier on yourself.