In my typical "worst case scenario" benchmark mission (a heavy Liberation dynamic campaign mission in the Tomcat, sitting on the ground), just turning Tacview off gave me back 7-10 FPS. In my case, it seemed to be hurting my CPU frametime with almost no change on the GPU side. These numbers are from the 2.5.6.50979 open beta in VR. I don't have any numbers to back this up, but I don't remember Tacview having this kind of FPS hit a few versions ago.