Since they have been updated with 5w chips the 600w Old Style panel consumes around 270w , The 300w about 140w. The Mars II and reflector series gained 5w chips too but did not lose wattage in the process.
I say because the 3w chip panels before the upgrade consumed 360w and 185w
Reason is they use less 5w chips in the old style panels then they did with 3w chips ,but not in the Mars II / reflector series.
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Onward and forward
Using 1 of the 300w old that draws 140w in your 2.5x2.5 works out to*46w per sq ft*
A very nice percentage !
I think the Mars II 400 would be too Powerful for your space after thinking on it.
I am using some Mars old old
version 100x3w Panels with great success.
They tell you to be between 30 and 50 watts per square foot.