However much you save on electricity, you will lose several times over in infrastructural costs. You will need more cards to get the same speed, meaning bigger and/or more motherboards in your miner.
Additionally, overclocking the 750 is a big no-no. PCIe power draw is capped at 75W, while this card draws 68W already. So unless you get an auxiliary power connector for every card on your miner, get ready for the lovely smell of well-done PCB. Even if you supply the 750s with the right environment, they are still budget cards and will not survive as long under a reasonable overclock.

Methinks the author of the article has never dealt with building a miner himself and all that impresses him is the hash-to-watt ratio.

I agree with Wirel though, a high-end Maxwell GPU might be well worth considering. A bit like what AMD did with the HD 6*** generation - slightly slower, but much more power efficient than the HD 5***.

Count me in for another 10k for the retrieval bounty. Phonetic seems to have done nothing to mend his reputation.