The amps I use have dual amps in them so I run two cabs per amp channel. This would be 4 ohms per side. the remaining amp gets the one cab per amp channel. The sound is stellar. I am moving and need to let go of stuff that will not fit in my new place so the cabs have to go. You can see my other listing here that have sold.
What I do to be safe is use two amps of the same type. For example, I have in a 4 space rack 2 SWR Working Man 300's I hook up 2 cabs per amp and the spread sounds amazing. I use a Boss Line Selector Pedal to run a cable to both inputs of both amps simultaneously. This is what I do for large rooms.