I use the non-dimmable ATI sunpower over my 90 gallon as well. 8x54 watt 48" fixture. I could have used the 6 bulb and hung it closer to the water and had comparable results, but I like the color combo options with 8 bulbs vs 6. And since mine is perched on top of a canopy, there is no wasted light due to spillage. The 8 bulb 48" is nearly the same footprint as the tank itself though so you'll want a canopy of sorts to capture that light from the outer bulbs.
If you're not using a canopy, you could probably get away with the 6 bulb 36" fixture and hang it 8" over the water and still get pretty decent coverage. I wouldn't do it for an sps dominant tank of course, but for your proposed stocking I think that should be perfectly adequate.
As far as a 6 bulb combo, having seen the new Giesemann bulbs, ATI bulbs and KZ bulbs, I'd recommend trying out 3 Giesemann actinic blur, one Giesemann super actinic, one Giesemann super purple, and one ATI coral+