Iron Fist - The power of punching moves is increased by 20%.
In the first Power-Up-Punch = 40 Base Power x 1.2 = 48 BP
In the second attack it will be 48 x 1,5 x 20% = aproximatted 80-90 BP
If you see, Close Combat is better, giving a 120 BP. Also Infernape doesn't have much defense and have much weakness like ground, water.. that are very common in competitive.
I suggest you to use Power-Up-Punch in a Mega Kangaskhan because hit twice, doubling the attack boost and Close Combat in Infernape.
Also you have a priority Mach Punch on Infernape.