That particular case is 19.61" x 10.24" x 20.67
I like small cases.
You can go smaller if you buy a M-ATX or even ITX motherboard.
For M-ATX, I like the Silverstone PS-07 14.73" x 8.27" x 15.75"
It has superb cooling and will fit any cooler.
For a ITX motherboard, I like the lian li cases; a Q01 case will hold a GTX960, but you are going to need a low profile cooler.
I might suggest a i3-6100 which comes with a stock cooler and is appropriate for a GTX960.
The case is only 10.83" x 7.87" x 9.53"