With the 22" depth, you may be good to go, with the Pro version. I'd keep researching until you are sure.
From what I've read, the high-powered LEDs give off a lot of heat too, though I'm not sure how they compare to metal halide. My hood is fully enclosed as well. I have two silent fans. You often see them marketed alongside metal halide lights. One is mounted low, at one end, and sucks new air in. The other is mounted high, at the other end, and blows hot air out. Works great and is dead silent. I also love the natural look of a single-point light source. It looks like sunlight. I'm attracted to dirt-simple, old school, low-tech stuff.
I must say I am enjoying your journey to affordable LED lighting. With the bewildering selection, it's a real challenge. The cheap ones are a joke, and even some of the premium ones I've seen at my LFS did not impress me. So I'm waiting and watching, on LEDs, for the right price and the right characteristics.
That reminds me, in the aquarium hobby, we often pay a higher price for the same things that are cheaper elsewhere. For example, I saved about $100 on my electronic ballast by buying it from a horticulture site. I would imagine LEDs are a hot item in that area as well, so you may want check 'em out.
Thanks for sharing. This is a subject a lot of us are interested in!