Since i upgraded from BIAB 2014 to BIAB 2016 I've noticed a considerable sluggishness in response GUI wise.

Anyone else noticed this ? Switching between any of the four mixer tabs on the top right takes about two seconds for example.

Everything else on my relatively spartan - minimal latest version macOS Sierra install runs fine..

iMac 2011 - i5 2.7Ghz 16GB RAM, tons of hard disk space

There are apparently some issues with Sierra and, for me, particularly so with the most recent upgrades. It's my understanding that PG Music is aware of the problem and is working on a solution.

Yes, this issue is sierra specific, and we are working in it. As you mentioned, certain functions like changing mixer tabs have about a 2 second delay.