I've got a 2/0, 3-phase, 120/208 feeder, so in Y mode that's 200 amps x 120 volts x 3 legs = 72,000 watts. That's only 1.44% of 5 MW. But in Delta mode that's 200 amps x 208 volts x 3 legs = 124,800 watts. That's still only 2.4% of 5 MW if I'm doing this right. I don't think that would even warm up this load bank up enough to spin the fans. But I can dream, can't I?
Not to be a stickler here, but 3 legs at 208 is the same amount of power no matter if you're running delta or wye. The formula for three phase power is Volts (line to line) x Amps x √3
For your 120/208 200A feeder, your available real power is 72kVA no matter how you slice it.