Video cards - GeForce 960 verses 970; and 7 inch verses 13 inch lengths?

I'm thinking of buying a decent video card. The only thing is, I want a compact one, if it will do the same as the long cards do. I don't want a card 12 or 14 inches long - 7 inches sounds just right. I'm using a 7 inch Radeon 7770 right now. I'm thinking of getting a GeForce 960 or 970 that is 7 inches long. Is there much difference between a 960 or 970 that is 7 inches long, instead of the standard 12 to 14 inches?

My power supply is an 850 watt Thermaltake Black Widow - plenty of juice for anything. :)

My current screen is a 27" 1920 X 1200 resolution. I expect my next screen to be bigger.

My current processor is an Intel i5-3570K, the best i5 in the Ivybridge line.

I don't usually buy a whole computer system at a time. Usually I upgrade piece by piece, one thing at a time. The graphics card is supposed to last this computer, the next computer, and maybe even the one after that. I want to buy one that will do the job 4 or 5 years into the future. That way I can afford an Intel Skylake processor, motherboard, and DDR4 RAM in a year or two.

Is a GeForce 970 worth the price of $325 or so? Would I notice much difference if I bought a GeForce 960 instead, for $190? Both cards come in compact versions, which are only 7 inches long, which is what I want.

To recap, the questions are, is there much difference between the 7 inch card and the 13 inch card, and is the 970 worth the large price difference over a 960?

Many thanks, ~Cindy! :)

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