I'd definetly go with 90's. With 2 2040 or 2 2060 you will have great end to end coverage, your tank is 18" front to back, so that's no problem and 90's will give you good depth penetration.
The one thing you might think about (I'm even considering it) is that 90 degree lenses makes the light very 'focused' or beam like, shining straight down. I was used to the MH, t5 and led strips I had really scattering light everywhere. With my old lights, even the shadows were soft due to bounced and reflected light as well as multiple sources. I find the leds create a look that has much more 'contrast'. The rock are as bright or brighter than ever, but the shadows under rock edges are much darker than before. I think it's because the light is so focused.
I moved my lights forward in the tank to get better lighting down the face of my LR wall and to try and light up the shadows a bit better. That spilled some light out the fron glass and put the rocks near the top of the wall in the back into more shade than light. So I tipped the lights toward the back just a bit. Now the front sand is lit, but no light spills out, the shadows have been reduced (some, but not as much as I would really like) and the rocks at the top of the wall in the back are lit better, and after all, they are only a couple of inches under the water surface.
Now I'm thinking of pulling a few lenses off some of the front row of leds and maybe some in back as well. Taking them off the front may reduce the contrasty bright rocks and dark shadows by spreading more light around and filling in the shadows some. And along the back to better light the upper wall corals, and I don't need penetration as the water is very shallow back there. I don't know if that will help, but when I get my 120 degree lenses, I'm going to try it.
But moving the light forward a few inches and tipping it back a few degrees reduced the super dark shadows some. And it reduced the glare seen under the lights when sitting in the same room and looking at the tank. Two of my lights are under a canopy so it doesn't really matter, but my 3rd light is hung over the anemone tank and has no canopy. After making this adjustment it makes the tank much easier to look at, especially in a dark room. I highly recommend this set up for anybody not using a canopy.