head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is variance, and it is a single point.

Execution · Practiced Mastery
The original top-down crime sandbox where you rack up points causing mayhem across three cities.

Optimization · Practiced Mastery
A tense survival horror where one bite kills your survivor for good.
Grand Theft Auto leans Execution (Practiced Mastery); ZombiU leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto
Twitchy top-down driving and shooting under police pressure
ZombiU
Deliberate cricket-bat timing and panic inventory management
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto
Cops follow simple scripts; nothing adapts
ZombiU
Zombies shamble on fixed logic
ZombiU leans a little harder on variance, though the gap is small.
Grand Theft Auto
Chaotic traffic and wanted-level escalation surprise players
ZombiU
Permadeath runs face unknown spawn placements
ZombiU leans a little harder on optimization, though the gap is small.
Grand Theft Auto
Score targets reward learning missions and city layouts
ZombiU
Route knowledge, supply caching, safehouse planning
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.