I read a post in this forum of new Z lenses coming from Nikon in 2021. I shoot with a Nikon Z6 and have three Z lenses at present; 14-30, 24-70 and 85 (the latter which is stupendous).
I miss my macro from my DSLR days and am anxious to get 'back in the game'. It's the close focusing that I love about the macro. I don't do bugs and stuff. I will acquire a macro but am not certain of the focal length. On my DSLR I had the Tamron f/2.8 90 mm. I used a crop sensor camera and therefore my lens converted to 135mm. Since I never used that lens for anything but close up and photographing my wife's art work (maximum distance was 6 feet), the reach was not used. A long introduction to my query:
If Nikon releases both a 60mm and a 90mm, what are the factors to consider with respect to the focal length most appropriate for me?
Thank you

The Nikon teleconverter will not improve the image on your Sigma, it can only degrade it. Same with the Sigma teleconverter.
There has not been a teleconverter yet made that improves image quality.
I strongly suggest you work on getting closer to your pray. Also get a cropped sensor camera that will basically do the same thing. And if you have a cropped sensor camera then you really need to work on getting closer to your pray.
Any teleconverter will darken your image and cause your auto focus to slow down. Never a good thing.
Most teleconverters work best on Prime fast lenses like a 300 2.8, 500 4, 600 4, they work next best on fast zooms like the 200-400 4, or 70-200 2.8, they work WORST on slow zooms like a 200-500 and a 150-600.
TIMHO.