I don’t know. I believe it depends on the settings of the material (different settings lead to different shaders being generated). In general I think that PBR shading is per-se more expensive.
If you are not fill-rate limited (eg. you don’t have a lot of overdraw or too complicated shaders) I think you wouldn’t notice in todays modern hardware. You may notice on mobile, where fill rates are usually more of a problem, or in lower end graphic cards with less powerful shading capabilities.
Again imho, If you are fill-rate limited, then you’d notice a FPS increase by avoiding PBR materials, but then you should first try to avoid overdraw. If your target is mobile, you may wish to avoid PBR, HDR and postprocessing entirely. Your game runs at 60fps on my hardware but I have a reasonably decent gear
But it’d be nice to hear opinions from more exprienced people. I’m kind of in the same situation myself.