I understand that, Graytail. In this case there are four COBS and many driver choices. And the driver may be most efficient at max but the COBs are more efficient (to a point) when under-driven by dimming.
I was rereading this and I don't think you really got an answer to your question.
It's partly because I know that it took me quite awhile to absorb all the info, so it's hard to sum it all up - there are a lot of numbers to go over. When you say that COBs are more efficient when they're "under-driven", I think I get what your asking. You have to go over the Lu/watt numbers for various COBs at various currents. If in your case you've already decided on 3590s, then choosing a driver is pretty simple. The one caution I'd make is not to get a driver that gives you
more current than you need. These COBs put out much more light than we're used to - there's no need to go past 1200 ppfd (about 130,000 COB lumens in a 4x4) unless you have a fantastic environment with control over everything. Without that, you'll just have the ability to thoroughly toast your plants with all that extra light.
Decide how much light you need and get those drivers. 50 watts per square foot is as much as you "need".
Then it's a matter of efficiency. Bigger COBs are more efficient, sometimes shockingly so. All of them become more efficient as you lower the current, roughly 7-9 points every third. If it's 160 Lu/w at 1400ma, then it's probably around 168 at 1050ma, and 176 at 700ma. Roughly - just a rule of thumb. 50% efficiency is somewhere around 160 Lu/w.
The driver really isn't involved in the more important design decisions. First multiply your sqft by 50 watts and get your total wattage, then work with various Lu/w for different COBs at different currents. Drivers can complicate things when you're deciding whether to run 4 or 5 or 6 COBs off each one, but once you've chosen your configuration for the number of COBs and how hard you're going to power them the driver choice is pretty obvious. All of the MWs for instance are equally efficient. The watts per dollar is slightly better on the 185Hs and the 240Hs.
The only other complcation I would mention is whether to use constant current MeanWells, or a cheaper non-dimmable driver, or even individual drivers (85% efficient vs 95% for the MWs), dimmable and not. There's a configuration for instance where you use one large driver to power all the COBs at a constant voltage and then use simple individual power amps to deliver the current you want. You can make it complicated, but at this stage of development the good choices are narrow. The MWs are very efficient and trustworthy, and they keep everything simple.
The other thing I'd like to mention is that it can be tempting to get way into the weeds chasing small improvements in efficiency and missing others. The difference between 160 Lu/w and 156 Lu/w is only 3%. You can lose that much by dimming the driver down past 80%. You can lose than much by letting a sink run a little too hot.
Oh, and another thing. The temperature of the chip has far more to with the sink than it does with the current level. When you lower the current on a chip it doesn't run any cooler - it just doesn't heat up as much given the same size sink. If you're dimming a larger driver to get the lower current, you're probably not getting enough additional efficiency from the chip to make much difference. You'd be better off simply moving more air over the sinks.
I may be a lil loaded, so sorry if that was a ramble.