[trilinearmipmap]

Well I have run an 8-bulb Tek light on a 48" x 24" x 24" 120 gallon mixed reef for around 5 or 6 years so you may find my experiences helpful as the tank you are planning sounds about the same as mine.

Softies: no problem. Mushrooms don't do well ? too much light or too low nutrients.
LPS: grow excellent
BTA's: grow excellent on the bottom of the tank, got one off Sam 5 years or so ago, now I have around 8 BTA's in 2 tanks, if anyone wants a BTA.
Clams: never tried them, if I had room for a clam I would get a Derasa or if it were a more light-demanding clam I would place it high up.
SPS: Montipora digitata grows like a weed on the bottom of the tank. Montipora confusa grows slowly on the bottom of the tank. Montipora capricornis at the middle of the tank took over 1/2 the tank until I hacked it back severely. One other SPS I tried didn't do well and eventually died, I think that was due to calcium or other issues probably not the lighting.
I have not tried any of the more difficult SPS mostly because I don't have the time to keep on top of frequent monitoring and testing of parameters etc. The tank is on autopilot and doing OK.

In summary if you want a mixed reef the Sunlight Supply 8-bulb T5 Tek-light is a good choice. If you were going to focus more on SPS I would look at a PowerModule.