re: optics.
could you mix them up if you get more than one bulb?

I believe the current AI fixtures have 40 degree optics towards the center and 70 degree optics towards the outside. I think that's a good idea.
Single source lights (like MH) create more glimmer lines than light with a wider spread (think T5 = zero glimmer lines) so I found the combo of 40 and 70 quite nice on the big tank.
That being said I have 40 degree optics on the DIY seahorse fixture and I don't see it with the bare eye but there's two things coming into play:
I have the fixture fairly high up to accommodate the mangroves so the cones overlap more I am sure
and
I can see it in photos but not with the naked eye. I guess my brain blends them but my Canon doesn't. lol

If you want the fixture close to the water then why not go with 60 degree optics and not have to worry about making a decision? ;)