I would say you need atleast three bulbs to cover a 40 breeder with "high light".
I know alot of people would say thats overkill, but its an 18" deep (front to back) tank and just to get proper coverage I think you need at least three bulbs. If your growing HC then the light needs to be strong all the way to the substrate, and presumably needs to be strong in the front of the tank even with the light sitting farther towards the back. I like t5's and I decided to do a led/t5 combo on my tank. I would try:
Its only two t5's but the added led is probably equal to another t5 bulb and the leds will increaes coverage because they dont have lenses. Id go 1 geisemann midday and 1 aquaflora. With the leds, its a nice bulb combo.
Just as a reference I havea 65 gallon which is the same footprint just 6 inches taller and use
and I still worry about getting good light in the front of the tank where the HC is. Cool thing about catalina fixtures is that they take either t5 ho or NO bulbs so if you decide the ho is too much you can scale it back.
I have no experience with the finnex but I know they use low wattage emmiters and if your looking for high light you should go with the ray 2 (If it were me Id use atleast two of them). I know that wpg is considered useless in this fantastic modern age, but at the end of the day a 36" ray 2 is only 29 watts and although Im sure it will grow plants Id be nervous about attempting an hc carpet with a single fixture.
The other thing you might consider if you want to go led is using two kessil amazon suns. I love the chip leds and think they are the future of aquarium lighting, and you could pick up two of them which is plenty for your tank for about $500. Aside from a great color rendering theyre really cool looking lights that will make the display stand out.
The maxspect razor 8,000k will be available in the US in a week or two. I think the 120w would be sufficent for your tank, and youd definately be the cool kid on the bus if you bought one. This light is awesome. At that price point, nothing else comes close imo.