Since you are copying tha same data to all rows, you don't actually need to loop at all. Try this:
Sub ARRAYER()
Dim Number_of_Sims As Long
Dim rng As Range
Application.Calculation = xlCalculationManual
Application.ScreenUpdating = False
Number_of_Sims = 100000
Set rng = Range("C4:G4")
rng.Offset(1, 0).Resize(Number_of_Sims) = rng.Value
Application.Calculation = xlCalculationAutomatic
Application.ScreenUpdating = True
End Sub