Centre sharpness remains high through from f/4to f/11, with f/16 and particularly f/22 being adversely affected by diffraction. The edges aren't quite as sharp as the center, with f/5.6-f/16 producing the sharpest results.

http://www.photographyblog.com/reviews/sony_fe_90mm_f2_8_review/

https://luminous-landscape.com/sony-fe-90mm-f2-8-macro-g-oss-hands-on-review/

In stock now in US

http://www.amazon.com/Sony-SEL90M28G-2-8-22-Standard-Prime-Cameras/dp/B00U29GNEG/

Our review sample of this lens proved to be exceptionally sharp, even when used at its widest aperture setting of ƒ/2.8. When used on the NEX-7 with its APS-C sensor, the images shot were tack-sharp from ƒ/2.8 onward.

http://slrgear.com/reviews/showproduct.php?product=1786

http://www.focus-numerique.com/plaisir-yeux-sony-fe-90-mm-2-8-macro-oss-news-6968.html

I'm definitely thinking about getting this and selling my current A-mount Sigma 105mm f/2.8 HSM Macro. Should be smaller with better performance.

But I wonder if the focusing will now be linear so you can rack-focus between two marks accurately. I hate that my 55mm f/1.8 FE has variable focus (1/4 slow turn on the focusing ring will hit different focus marks vs 1/4 fast turn)