What is most important for getting super FPS in Morrowind? GPU or CPU? I have a core i7, gtx950m card.

Depends on which and how many mods you want to use... Morrowind alone is 13 years old and should run on just about any hardware. But there are tons of graphics and gameplay mods available and they can have a significant impact. Up to the point where your hardware again almost does not matter because the engine itself is not meant to handle this amount of high-res textures/NPCs/scripts/etc... and there is not much that can be done about this. High-res textures and meshes are usually not a big deal, if not completely over the top (there are some "better meshes" mods around that subdivide simple meshes into thousands of polygons but do not actually improve their look), but in combination with e.g. MGE XE, NPC and creature mods and some script-heavy gameplay and quest mods, the best hardware will fail to deliver high frame rates. The most limiting factor is the CPU, usually, because Morrowind cannot use more than one core. But as I said, there is a point where the engine cannot handle all that stuff smoothly any more. Hopefully, OpenMW will change that in the not so distant future.