There's nowhere near 40% difference in efficiency between a 750 Ti and a 970 because they are both Maxwell cards. The only way you'd get such a huge difference is if you use a memory bandwidth/latency hard algo (old lyra2) but for most algos a 970 is about 2.7-3.1x times faster than a 750 Ti which reflects their power consumption.
I have GV-N970WF3OC 970 cards which are virtually the same as the G1 ones and they never ever go above 60°C with 8cm gap between them.
The 1 fan 970 minis on the other hand would go 75+ if I'd let them but I use a 70°C temp target on them.
I plan on measuring the hashrate, power consumption, temperature for all relevant algos, for all the different type of cards I have with different power targets for a long time, I think I'll get to it later this week and share the results.
Not unless you use terrible HDDs to begin with like WD Green series which keep parking the head after 8 seconds of being idle and are only rated at 300.000 of these parkings.
60GB SSDs are not expensive anymore (and preserve their price better) and I'm still below 1TB total writes on them after 1 year of constant use running several wallets.
I have GV-N970WF3OC 970 cards which are virtually the same as the G1 ones and they never ever go above 60°C with 8cm gap between them.
The 1 fan 970 minis on the other hand would go 75+ if I'd let them but I use a 70°C temp target on them.
I plan on measuring the hashrate, power consumption, temperature for all relevant algos, for all the different type of cards I have with different power targets for a long time, I think I'll get to it later this week and share the results.
also, mining, kills hard drives like crazy, unless use SSD which are expensive here.
Not unless you use terrible HDDs to begin with like WD Green series which keep parking the head after 8 seconds of being idle and are only rated at 300.000 of these parkings.
60GB SSDs are not expensive anymore (and preserve their price better) and I'm still below 1TB total writes on them after 1 year of constant use running several wallets.
bathrobehero what is your regular ambient temperature?, I am in a very hot area, that could explain why my cards where working at 75C and yours at 60
I had 12CM spacing between them, and a 3000 rpm fan between every card to prevent that one card heat up the other one, still, in quark specially, it was impossible to lower the temperature below 70C, in lyra2v2 yes, usually where at 60 probably, don't remember exactly.
true WD Green dies fast! for offline storage they are ok, but not for much else, even if you modify the parking time (i usually do, to 30 or 60 seconds), I always use black or red drives which has better warranty and lasts longer too (one of the few companies that has true warranty in my country, WD, and is excellent!)
still mining kills a lot of hard drives, until i switched to usb flash, I killed about 10 or 11 wd black, reds, and seagate drives beyond repair, keep in mind that it is the mix of 24/7 operation, a LOT of power outages (here power is extremely unstable, we have short brownouts at least 10 per day) and at least 1 power outage a week, 1 of 4 may last days.
(reason why I spend a ridiculous amount of money in inverter generators, smart UPS, solar panels, power regulators, inverters, I even have a low voltage line across the apartment for the essentials (battery powered)) add to all that, high temperatures and high humidity and you get....HELL !! hehe
About the SSD, mining OS does not write a lot, just moving the logs and temps to ramdisk is enough, a crappy kingston V300 will last at least a couple of years easy.
of course someone mention that the 840 Pro still works, of course, it is one of the best SSD consumer drives in the market! I have one in my workstation and is fantastic and very fast!, but at almost twice the cost of the kingston, it worth it for your workstation but not for a miner IMHO.
I had an excellent experience booting of flash USB drive, almost all of my stability and disk problems went away since i boot off USB flash drive, so I will keep doing it
hehe. (I know i am a stubborn sob ) 
