Conclusion from Phillip Reeve:
Who is the sharpest of them all? It is the Sony FE 1.8/135 GM, at least for all lenses that I have used yet. It is the first lens where nothing happens when I stop down except of decreasing vignetting and increasing diffraction. Even the macro and microcontrast is completely there wide open.
Besides sharpness, I can also praise the good CA correction, low distortion, low vignetting and the close up sharpness.The proven GM build quality makes using this lens a joy, especially the large amount of manual lens controls is very useful.
I can say with confidence that this lens reflects a decent price/performance ratio and that this lens is a premium performer at a premium price tag.