Wattage will be variable but it's been demonstrated that 1500 PPFD is the maximum light intensity the plants can deal with before growth rates begin to decline. Even with COBs there will be some intensity variance across the canopy so keeping things under 1300 PPFD is a good idea.
6 CXB 3590s at 2.1 amps would provide 1350 PPFD in a 3x3, would be 453 watts dissipated, 231 PAR watts.
6 at 1.75 amps would provide 1145 PPFD (375 watts 200 PAR watts)
8 at 1.4 amps, 1285 PPFD, 398 watts, 223 PAR watts
10 at 1.05 amps, 1230 PPFD, 355 watts, 213 PAR watts
16 at .7 amps, 1360 PPFD, 368 watts, 235 Par watts
I'm thinking any of those 3 middle options would be really intense without being too crazy about it.