Arctic coils are either "Bottom dual coil" (BDC) or "bottom turbine dual coil" (BTDC). The recommended wattages for the different coil heads are as follows:
BDC:
.2 ohm: 20-50W
.5 ohm: 20-50W
1.2 ohm: 10-25W
BTDC:
.2 ohm: 30-100W
.5 ohm: 30-80W
50W seems a little high for the .5 ohm BDC, and 80W seems a little high for the .5 ohm BTDC, but that doesn't really matter with a Coolfire IV.
Basically, with that device, unless you're using the 1.2 ohm head you can go ahead and crank it up as high as you like!
Happy vaping