Does 2 x GTX 950 = 1 x GTX 970 ?

It doesn't really work like that. You will always get better performance from one big powerful GPU than 2 smaller ones with specs that add up to the big GPU. This is due to the way SLI works, there is overhead, games and drivers have to be coded right, it can add frame latency and lots of other fun stuff. In some games SLI actually can hurt performance.

Roughly correct, although it's better to go for a single, more powerful card. Also at this point the 750 Ti has been buried by the R7 370 in terms of performance per dollar.

This should answer your question, tho the answer changes a bit by resolution



And it changes by game... in some cases SLI scaling might be as high as 96% (Tomb Raider) ... on average it's 70ish%....some don't do well in SLI, at least until a new profile comes along and in rare cases, a game never gets one.



And yes, I know ya asked about a 950, but TPU didn't test the 950 but it's safe to say that if the 960 can't catch it in the summary, then the 950 won't either.

no, you really have to follow the "money" more than the perfomance....
+ 2x950 is not 50%+50%=100% you must take out the "over head"=(performance loss) it needs to connect and sycne data between the two in reallity you are getting more like a
2x950= 50%+30%+(20%in overhead gone) + the 970 performs with "4gigs(/3.5) where the 950 even two of then only still perform with tops 2gigs. because the same information must be loaded in the VRAM in each card so loose perface in the hi def (e.g 4k, ffaa.. ) area as well.
in addtion to that^^ above you must also have the correct hardward.
mostboards have 3.0 pciE 16x1 and 8x1 so for the "full" performance of say 2 cards you need (although opinions are split) a motherboard that supports 2x 3.0 16xPciExpress or in one of your mentioned examples 3x 16xpcie..
most motherboards that support such throughput are e.g expesive sky lakes are 250-500$ the g1 from gigabyte comes to mind or you need a X99 chipset with a CPU that has enough aforementioned lanes.
not to mention the power supply to drive to slower cards 950x2 vs 1 970.
i think honestly if you just happen to have the right setup then 2x950 would be ok but still not what you are expecting for shelling out 2x~400$
and a the way for a 750ti is not supported i do not believe those are supported in the higher hierarchy card 980 970.. and crossfire the pride theirselves on that the 3 way they got going anytime any place for amd which just now since the newest line up of cards even makes sense to think of.
if you need more power the honest to goodness best way to go about doing it is geting the card you want ^^ 970 and then you have the expected performance as well no letdows no tearing, no setting PC on fire, no thoughing money out the window only to find out that hindsight twenty twenty , you need to go and buy yet another card agian a year later.

and as i said earlier follow the money.. e.g. 2x970= 600$ = ~980ti
2x980=1000$= ~titatain X now if you really need more power, have boardum or money to blow wait for the next wave of card get two of those and while you wait buy two titainX's to tyi you over and when your done with those send me one.. <- last part was a joke.

but you can still sell you currently relvent 750ti 950 960 or what ever you have on ebay or here or school, work, return it... and get the card you want when you have the money.

im waiting it out there should be a new round of cards and some AMD cpus coming very soon.and you can get the next best thing then till then the 950 will more than suffice and i wold grabe the evga Xcealrtor and have OC you card for you in game and you'll have plenty of power.

http://www.game-debate.com/hardware/index.php?list=gfxDesktop
you can also compare EVERY card sli or not with what ever riight here enjoy knock yourself out it wil give you the excat %

970is 24%faster than 950sli.

24% due to memory
anything above res 1440 starts to have problems
http://www.game-debate.com/gpu/index.php?gid=3242&gid2=3154&compare=geforce-gtx-950-2gb-sli-vs-geforce-gtx-970-msi-oc-4gb-edition

That's the kind of question more suited for somewhere like the Folding forums, folk here see "SLi" mentioned and think it's all about the gaming. As I don't have any 950's I will have to speculate but based on the cards that I do have I reckon that two 950's would be about on par with a single 970 in processing power.