I think the EVGA pads are pretty soft. Like Shore OO 40 is what I saw somewhere. The thermalright pads are a different Shore scale (Sc 30-50). Sc30-50 is ~65-85 on the ShoreOO scale. The EVGA pads should compress more for a given mounting pressure. Or restated, need to be thicker to have the same contact pressure on a given clearance.

With that in mind, I'd probably go for the 2.0mm and then check for proper contact. 2.5mm may be too thick and hold the cooler off the GPU die.

I've seen 3.0mm being listed as the correct thickness to put between the back plate...