Okay, so I just found some performance issue when changing the FOV.
I am using an FInterp to go from something like FOV10 to FOV90 (sniper scope) in a matter of half a second. There is quite hefty FPS drop. Goes from about 90 (zoomed in) to under 10 (during zoom-out) to about 60-70 (zoomed out).
Anyone has had this problem before? Or a solution for it? I suppose it has something to do with culled objects becoming visible again but I am not quite sure. Any input appreciated.