The only person who appears to have done a side-by-side comparison is Paul G on Cloudynights who wrote (
http://www.cloudynights.com/topic/41...o-i-vs-zao-ii/)
"I've side-by-sided the I's and II's, both mono and binoviewing with the Mk V, in several scopes including the following Astro-Physics refractors and Mak-Cass:
92 mm f4.9
92 mm f6.6
105 mm f5.8
130 mm f6
130 mm f6.3
155 mm f7
175 mm f8
254 mm f14.6
I've seen no noticeable difference between the I's and the II's. It's possible that one might notice a slight difference in edge correction in a fast scope if one were observing in an area with excellent seeing, but that's not where I live. In our seeing here, no difference.
The real gems of the I's were the 25 and 34mm. I was disappointed they didn't include those focal lengths when they brought out the II's. "
The other aspect you might consider is that the ZAO I series have a nasty undercut in the draw tube, to the extent many found it objectionable.
