Well, your cab is 19 cubic feet, so I'd say the minimum fan you'd want to use would be at least 120CFM.

I have a cab thats 30x19x55 (22 cubic feet) and I have a 150HPS and a 70W MH in a hood. I use a 110CFM bathroom fan cut into the side of the cab, along with a 40 cfm thermostat controlled computer fan mounted in the actual light hood, that blows directly at the fartfan. Theres also a small moveable fan in there to blow directly on the girls. 2-4" Holes cut in the bottom and back of the cab to pull cooler air from the wall/ground area in a passive intake.

Temps are always dependent on intake/ambient room temps, but it never gets more than 8-10 degrees over ambient. This is a bad thing though when the ambient is 40 degrees (which is why I have a thermostat/speed control on the light fan)

Your best bet is to increase the exhausting of hot air - bigger exhaust fan or maybe your intake holes are too small? Or reduce the intake temperature somehow by moving the cab to a caooler location?