I've been trying to split Zeta Bootis for over a week, mostly when it was still too low in the sky, and with poor to mediocre seeing. Despite this the 20" f/5 consistently hinted at its double nature by giving some odd "non-stellar" diffraction patterns even though the airy disk(s) were not seen. It is hard to describe, but you've probably seen these sort of interfering diffraction patterns with other tight doubles in various apertures.
Finally tonight I succeeded as the double neared zenith. The seeing settled somewhat although still not good enough to yield stable 1st diffraction rings or stable airy disks in the 20" (which was well equilibrated, fan off for the observation.) The 8" SCT would sometimes get a relatively stable diffraction ring for a few seconds, so the seeing might have nudged 7/10 in the best moments, but more like 5/10 was the norm. The SCT was showing an elongated airy disk above 500x when the seeing would allow, but it wasn't steady enough to provide satisfying proof of the double.
The 20" finally paired with moments of steady seeing at 625x and 833x to cleanly split the airy disks for several seconds at a time. This was repeated several more times over the next 20 minutes. "Cleanly" is a relative term in this case because it means that a dark line was evident between the two clearly seen disks and always with the same orientation. There was still all sorts of motion around the disks but they were staying fixed relative to one another. As for PA's, I couldn't tell which one was brighter. They are very closely matched. However, they were offset about 10 degrees from the diffraction spike which was roughly aligned on the preceding/following axis as they drifted.
Separation was tight. It appeared over 0.3" but I couldn't estimate how much more because the diffraction rings were never stable enough to determine where they were centered relative to the center of airy disks. WDS shows 0.5" measured in 2015. Based on the appearance in the 8" and 20" scopes I guestimate it closer to 0.4" separation. What is the current prediction?