Its only ~720 lumens more per cob with cxb3070 BB vs cxb3590 CD 3500k 36v @ 1.4A. +18lumens/watt. With 6 cobs that is like half a cob extra light overall for these cxb3590s.
But considering the price difference of $32 vs $49 per cob. $102 additional cost for the 3590s, I'm probably reconsidering the 3070s now simply because they cut the up front cost down considerably at a marginal decrease in efficiency. 10% decrease in efficiency for a 35% decrease in initial costs.
$102 towards extra electricity "wasted" gets you 850kwh @ $.12 per. 16watts wasted per hour extra, 53,125 hours, 8 years @ 18/6.
So the money saved on 3070s beats the efficiency earned on the 3590s. The only other consideration is increased yield for added lumens but I'm not high enough for that kind of math.
Prices are cutters USD price cob only no shipping. Calculations for a 6 cob fixture
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TL;DR unless you can get cxb3590s for about $5 more than cxb3070s, the cxb3070s will be a better value overall. At a 2 year lifetime of 18/6.