Everyone worries about/discusses efficiency of hub gears. Nobody ever worries about or discusses the variable efficiency of derailleur set ups - even different gear combination on the same drive train. The typical comment treats all combinations in derailleur drive trains as the perfect base line to which to compare hub gears; the reality does not agree.

A 52/15 and a 38/11 are the same ratio, but the 52/15 is significantly (as these things go) more efficient. The gains are worth far, far more than the negligable grams of weight savings that everyone does focus on. In a review of over two dozen cycling books, not a single one mentioned this.

BTW, modern chains can run significantly out-of-line without meaningful effect on efficiency. The power goes into rotating all those little bushings under load, not flexing the links sideways. See the Kyle/Berto test, above.

HTH,
TCS