CMH are great lights!
But as for the LED stuff...
240W in a 3'×3' might be a bit under powered. For only ~$20 more I'd shoot for a 320h. Most recommend 35W/ft2. With a 320h if it's too much you can dim, with a 240h if it's too little you're stuck. Personally I use (2) 320h's in a 4x4.
240h means 240W, 320h means 320W ect.
I'd go with (4) QBs, 288s or bigger (QB288 = 288 chips, QB304 = 304 chips, ect), and then a single 320h. If you ever wanted to split into 2 seperate tents, or decided to move up to a bigger 4×4 you'd only need to buy an additional 320h driver.
(4) QB 288s or bigger, with a 320h driver is my suggestion. If you're trying to reduce electrical costs then the solution with the greatest # of total chips per wall watt is going to be your determining variable. You don't have to run all 320W.