I don't know if there's a genre title for this, it seems to cut across genres. What is your favorite game to sit down and create and test builds?
My favorite so far, by far, is Forza 4. The forza series has a few things that make it a fun build game. The rating system is vital because it gives you a limitation to work within. You build just under the rating cap and then try to find the right parts and tuning to maximize your performance at that rating. I spent hours and hours in that game making builds and testing them, then when you find the one that's just right, another hour making a cool livery.
The Armored Core series is all about this too. If you haven't played them, they're giant mech games but with hundreds of parts to choose from to build your core/next/raven. The different games have different stats but often you have to trade off armor or mobility or weapon power for weight, energy usage or heat. I loved this series because of the same thing. I could spend hours balancing parts to get maximum performance out of energy or heat usage then testing them against arena opponents.
If you are in to this sort of thing in a game, what are your favorite games for tinkering with builds and spending hours getting that extra 1% performance?