head to head
Grand Theft Auto: San Andreas asks more than Grand Theft Auto IV, and the gap is optimization.

Execution · Practiced Mastery
A grittier crime story where weighty driving and gunplay carry the experience.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.
Grand Theft Auto IV leans Execution (Practiced Mastery); Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery).
Grand Theft Auto IV leans a little harder on execution, though the gap is small.
Grand Theft Auto IV
Heavier driving and cover shooting reward control.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Grand Theft Auto IV leans a little harder on reads, though the gap is small.
Grand Theft Auto IV
Scripted AI, no adaptive opponent modeling.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto IV
Minor mission variance.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto IV
Mission routing and weapon picks learnable.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
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.