GPU computing cards and performances

I am trying to build a workstation with some GPU computing capacity. I am little lost with all the options out there. I need a little help. I will be using the computer for scientific computing. The options I have are

2 X NVIDIA® Quadro® M4000 de 8 Gb (Maxwell Generation 1664 x 2 cores, Compute Capability 5.2) 2 x NVIDIA® Quadro® K4200 de 4 Gb (Kepler Generation 1344 x 2 cores , Compute Capability 3.0) 1 X NVIDIA® Quadro® M5000 de 8 Gb (Maxwell Generation 2048 cores, Compute Capability 5.2 ) 1 X NVIDIA® Quadro® K5200 de 8 Gb (Kepler Generation 2304 cores, Compute Capability 3.5) Prices all around same. I am open to other suggestions.

Thank you

Erdem