I understand you have the 5A (which I also have). When I went to Best Buy and put both the 5A and 6A at max brightness, the difference between the two was marginal. This is not necessary a bad thing as the 5A gets plenty bright enough to be able to view the screen in sunny conditions.
In general, I fail to understand the need to have brighter than sun displays that many favor. While it's nice to have a bright screen I rather not burn through my retinas! On my 5A I always keep the brightness on auto and set it right at the middle when I want to manually change it. That's good enough for me.
After I use the 6 for a bit (once it actually delivers) I'll then decide whether to return it and stick to my 5A. Unfortunately there is a $30 fee for restocking fee charged by Google.