The 52 volt cob is more efficient, but not by a lot. Mostly your driver cob and cob matching comes down to witch cobs fill driver the best. If you’re target is say 100 watts, you can get around there with two 52 v cobs running 1000ma, four 52v cobs running 500ma one 72v cob running 1400ma, three 36v cobs running 1000ma, four 36v cobs running 700ma.
It seems difficult, but there’s just a handful of things to take into consideration. Target wattage, budget, led efficiency, and coverage. 4 cobs driven softer will provide more even coverage and higher efficiency than 1 cob driven harder. It will also drive your build cost up. Budget is usually the biggest factor, so you try to find a happy medium that works for you.
In your case, we’ll say you want three 300 watt bars. Your options per bar are 3 cobs at 100 watt each, 4 cobs at 75 watts each, 5 cobs at 60 watts, and we’ll stop there because we can all do that math. Each time you add a cob the build cost will go up, but the coverage and efficiency will get better too. Once you decide where you’re at with that, you look for driver/cob combinations that will work without leaving a lot of excess voltage available. As you originally stated, the 36v Vero and hlg-320-2100 give you that. I’m not sure that there is a better option in the Vero line using meanwell driver and series wiring. Possibly the 52v and hlg-320-1400, but I’d have to pull the data sheets and check voltages for compatibility.