How do I check if a graphics card is Maxwell or Kepler?

Thinking of picking up a Lenovo Y50 and it comes in two configurations, the GTX 860M Kepler or Maxwell. Now this one would be easy to guess because the Kepler is 4 GB and the Maxwell is 2 GB, but there are people who say on the internet that they got have an 860M Maxwell with 4 GB. I'm not sure whether there is an 860M Maxwell with 4GB, but I wanted to make sure that I get the 4 GB Maxwell instead of 2 GB Maxwell if there is one. Checking the GPU would be a matter of going to GPU-Z, but unfortunately I can't install it on the display units in the stores, so is there any other way to see if the card is a Maxwell or Kepler?

I'd ask the store helper, except that they're almost illiterate in hardware terms and they don't even know that an MQ processor stands for quad core and HQ is not octa-core. All they do is tell me they got an extended warranty available and the processor is an i7 (which, according to them, is always better than an i5 xD). Also, is there really an 860M Maxwell with 4 GB configuration, or just 2 GB?

Its maxwell, it uses GM107 core.

So there is no 860M configuration which is 4 GB and Maxwell?

I thought Maxwell was Intel CPU. Think I am behind in GPU makes lol.