head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Practiced Mastery
Piloting skill plus careful fuel and ammo routing across scripted missions.

Execution · Practiced Mastery
Planning and flawlessly executing long infiltration routes with no safety net.
Nuclear Strike leans Execution (Practiced Mastery); Project I.G.I.: I'm Going In leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Nuclear Strike
Helicopter piloting and aimed strafing under fire demand steady hands
Project I.G.I.: I'm Going In
No mid-mission saves makes every shot and sprint count
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Nuclear Strike
Enemy emplacements follow fixed scripts
Project I.G.I.: I'm Going In
Guards follow alarm scripts, punishing but not adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Nuclear Strike
Map layouts are unknown on first pass only
Project I.G.I.: I'm Going In
Patrols vary slightly, mostly memorisable layouts
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Nuclear Strike
Managing fuel, ammo and mission routing is the real layer
Project I.G.I.: I'm Going In
Planning infiltration routes through bases is the core test
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.