How significant is going FX from a DX?

I have been shooting for the past 2 years with my nikon D5200, over that period I have collected a range of lenses namely the tokina 11-16mm 2.8, sigma 17-55mm 2.8, the nikon 35mm 1.8 DX and 85mm 1.8. 
I'm considering going full frame as the camera isn't nailing focus as fast/accurately/sharp as i want to. I'm considering getting a d750 and using my current body as a second body when shooting events, lens wise i would have to narrow down between getting the tamron 24-70mm 2.8 or the Sigma 50mm 1.4 Art lens. 
I would like to ask how significant is this transition and if you think that it's worth the money, if so, which of these two lenses should I get? 
I usually shoot portraits, events and landscapes.

Thanks!