I wouldn't put much stock in that claimed 1.1lb weight difference unless their is something other than the barrels that are different. At best on a heavy contour barrel with deep flutes you might shave 6 ounces of weight with the flutes. The factory flutes are fairly shallow, more so on the fluted sporter barrels. If they shave off 4-5 ounces I would be surprised which is a far cry from 1.1lbs.
As for heat buildup, I don't think it will make much of a difference. The fluted might cool a little faster, but that's about it.
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