I have the 70-200 gmII and the 200-600 I usually use the 1.4tc on the 200-600 but i always seem to "want" more.
I have not used the 1.4 on the 70-200 yet but I would assume its good........ Do I really need the 2.0TC???? or is this more of over gearing
It depends on how much the reach is important to you. I actually struggled so much with the TC decision as well. I ended up getting the 2.0 TC for the reach. The problem with the 2.0TC is you sacrifice more stops of light. Ideally, you need to be in pretty bright conditions for good image results. I heard overall 1.4 TC had better image quality than the 2.0TC
I agree with Caroline. TCs always add optical aberrations of their own; they cannot make anything sharper, just upsize the center of an image. Cropping a high-res sensor, or even shooting with an APS-C camera, is better than a TC.
In my case I use the a6000 as a backup to my a7iii and can thus use it as a simple "TC". The main disadvantage is roughly the same (light loss per pixel) but with no extra optics in the light path, quality should actually be better.
If you have the money for it, it's a 'nice to have' in certain situations but if you already have the 1.4 then you're not really missing out on much. I do love it with my 70-200mm Mk2 though; it's nice having a 400 f4 with super fast AF.