I'd still take the 2 Sp150s in a 2x2x3 or 3 in a 3x3, I don't care about the lack of a dimmer and I don't have room for a rectangle tent...
Whatever suits you the most
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Not trying to put down your opinion, but personally for that amount of money i would get a Migro Aray or Lumatek/Photontek for 2x2 or 3x3. Better quality lights, customer service, warranty and results.
And i'm not sure about your electricity prices, but in my case running the lights at full power without a dimmer for 3 months or so, i think the bill for the total grow would pay for the difference in pricing between the lights. (especially now when energy prices are going up)
And the high blue spectrum in SP150 probably wouldn't produce as much as other lights with more red spectrum.
Not to mention the trouble of possibly burning the plants without a dimmer, the constant heat etc.