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.

Optimization · Pure Optimization
Optimizing city placement, social policies, and victory routing under randomized map unknowns.

Optimization · Pure Optimization
Mastering interlocking social engineering and tech-tree systems on a programmable alien world.
Civilization V leans Optimization (Pure Optimization); Sid Meier's Alpha Centauri leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Civilization V
UI actions need no precision; speed is not a factor
Sid Meier's Alpha Centauri
Turn-based; no twitch element at all
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Civilization V
AI follows scripted personalities, not genuine player modelling
Sid Meier's Alpha Centauri
AI faction leaders follow fixed personality scripts
Civilization V leans a little harder on variance, though the gap is small.
Civilization V
Random starts, barbarian spawns, and goody huts create hidden unknowns
Sid Meier's Alpha Centauri
Xenofungus and psi combat add some irreducible randomness
Sid Meier's Alpha Centauri leans a little harder on optimization, though the gap is small.
Civilization V
Hex placement, social policies, and victory routing are fully solvable
Sid Meier's Alpha Centauri
Tech tree, social engineering, and base placement are essentially solvable
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.