The heat range is the last "number" in the part number
2.9l uses Motorcraft awsf 42 c spark plugs
C = copper, P here would be single platinum, PP would be double platinum
42 is the heat range, lower number would be colder plug, this means the spark plugs will cool off faster, you often go colder to prevent pinging or if super or turbo charging.
This doesn't lower cylinder temps, just keeps spark plug tip from getting red hot under load.
32 would be one heat range colder not 41
Hotter range, higher number, can prevent fouling from carbon caused by oil leaking in the intake valve stem, but it can cause pinging if spark plug tip retains too much heat, red hot spark plug tip will pre-ignite air/fuel causing pinging.
So to answer the question you would run awsf 44