I have similat problems. I have 6Gb DDR2, Intel core2Quad, Geforce 650GTX. I think that GTX 750 not more speedy that 650. Better will be GTX950. And of course 8 core processor and 16Gb memory. I agree it will be more good.
Maybe EU4 have options for disable full shading in editor? It’ll be a long time before it is at least pre-compile the game. And to work in the editor always with 100% elaboration of the Shader is not so important.