For MATLAB, unless you are doing strongly divisible operations such as Monte Carlo sampling, you are better off with one really powerful GPU than two less powerful ones since you can only use them for that kind of thing (see http://blogs.mathworks.com/loren/2013/06/24/running-monte-carlo-simulations-on-multiple-gpus/).
So you probably want the M5000 or the M5200. Choose between those based on whether you need double-precision performance or single-precision performance - the Kepler card will most likely give you far better double-precision performance (and MATLAB uses double precision by default), but if you can get by with single precision then the Maxwell architecture will give you more lastability.