Keep in mind that tent isn't actually a 2x2. It's 2.3x2.3(70cm x 70cm) so it's slightly bigger. As for the comparison between the Mars COB and the Optic 1 XL, they have about the same efficiency but the Mars one has extra blue and reds on it and the spectrum is very oriented towards the flowering spectrum. The Optic 1XL is a straight 3500K spectrum, no extra reds or blues. That's the biggest difference.
Don't buy the Optic 2 for your tent, it's too powerful. What i am talking about is the tent height, around 5 feet. The Optic 2 ran on full blast will burn your plants at 18 inches(over 1100 PAR), it's that powerful. You have to run it at around 24 inches if not higher. As for dimming it down, that won't really work the way you think it will...
Dimmability: 3 possible settings
Channel A: Just the COBs (Pulls 120 Watts)
Channel B: Just the Bloom Enhancer LED array of 5w LEDs (Pulls 100 Watts)
Channel A & B: The COBs & Bloom Enhancer LED Array (Pulls 205 watts)
So if you turn off channel B, which you'd have to do for that short tent, you'd end up with straight COB at 120 watts or in other words the Optic 1 XL would do the same job and do it better(it's more efficient, got a better Cree chip). If you want to go for the Optic 2 then get a taller tent.
My 2 cents.