So perhaps this is a bit off topic, but you guys seem like a knowledge group. Are the 750 ti's the most power efficient of the of the Maxwell cards? Thanks.
It greatly depends on where you live; for me the 970s are the best choice by far even if I only go for 4 x 970 per rig, but of course I also add 2 x 750 Ti.
While a 6 card 750 Ti rig looks great on paper, you can't really disregard the price of the whole PC itself (mb+cpu+memory+hdd+psu) which all adds up, disrupting the efficiency/ROI of a 6x750Ti rig. But of course YMMV.