Comment by jbinto

It's good to see this get some attention. I spent a long time trying to figure out how to make full screen zoom usable with an external display.

I found if you enable the "Increase Contrast" accessibility feature, performance is improved, but it does negatively affect aesthetics.

I answered my own question about this on Apple StackExchange here:

http://apple.stackexchange.com/a/157118/70049