Light spill is a hard one to solve/consider when setting up lighting. I really like smaller dimmable 12v jewelry case spot lights set right on the glass to get the same effect you would get with track lighting on longer tanks. Being a planted junky though; focused spot lights are something I only add during my twilight cycles (bourbon time for me), and only when I have company. I have to tolerate the ludicrous brightness most of the day and it's enough overall that it doesn't really matter if it's my above tank light bars or the flush ones, the room glows like the sun.
The problem I have with my flush/set on top bars (or the mini spots) is finding a temporary home for them when servicing the glass lids and working on planting in the tanks. Hard to plant in the dark and my above tank lights make that allot easier.
I think if I were setting up a tank as large as 8x4 and had a modest budget, I would build a modular grid based (think theater) 12V spot and flood system, likely hinged off the wall behind the tank so it can be swung up and away. Probably set it up with 2-3 individual power supplies on individual timing circuits, and spring the little extra for focusable RGB mini spots, this could give the primary viewing lights (not grow lights) RGB washing and really get some glitter out of the fish. A separate circuit for twilight floods and the third circuit for grow and or uv lights as appropriate.
With a big budget I would build that whole thing into a gas shock assisted hood, but in addition to the materials to build one, you would need active ventilation and other noise magnets to keep things cool and in ideal humidity and that would distract me (personally) from the immersive nature of the tanks I build. One of my power supplies (the grow lights in the original rack) has a thermostatic controlled fan and it drives me up the wall if I'm focused in on something and it turns on surprisingly.