Coil UVB lights are probably the least effective UVB producers. A T5 High Output linear UVB bulb that has been correctly fitted with a reflector, will produce as much UVB, if not more, than a mercury vapour lamp. With this level of UVB, distance to the basking spot is a critical factor, yet it has not even been mentioned. I don't know why. No mention either of whether this is to be placed inside the enclosure or above on a grid roof. The orientation of perches under such a strong UVB source should also be considered, to avoid potential eye damage. I’ll leave it those more experienced to provide fuller guidelines in these respects.
PS. IMO wattage does not need to be considered here. What is paramount is what is needed to provide adequate UVB exposure. T5 UV linear bulbs are the most energy efficient at producing UVB. Their effectiveness is dramatically increased with the use of an appropriate reflector hood. Bottom line, using these, especially the HO bulbs, you will be getting the most cost effect delivery of UVB light.