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

Execution · Pure Mechanics
A rally racer where mastering precise car control against tricky terrain is everything.

Execution · Pure Mechanics
Reflex-driven point-to-point racing through heavily scripted setpieces.
Colin McRae: Dirt 2 leans Execution (Pure Mechanics); Need for Speed: The Run leans Execution (Pure Mechanics).
Colin McRae: Dirt 2 leans a little harder on execution, though the gap is small.
Colin McRae: Dirt 2
precise rally driving and braking required
Need for Speed: The Run
Reaction driving through traffic and setpieces is the test
Need for Speed: The Run leans a little harder on reads, though the gap is small.
Colin McRae: Dirt 2
no adaptive opponents, mostly time trials
Need for Speed: The Run
Rivals rubber-band on scripts, nothing to out-think
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Colin McRae: Dirt 2
weather and surface conditions vary
Need for Speed: The Run
Scripted events surprise once, then are known
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Colin McRae: Dirt 2
car tuning and racing lines solvable
Need for Speed: The Run
Checkpoint routes and car choice are quickly solved
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.