Content download time relatively high

[pmeenan]

+1 to SPDY (or better yet, HTTP/2). You might need a reverse proxy in front of nginx like H2O but it will make a world of difference because it will eliminate the dead time setting up the new connections.

Also, spend some time here: https://istlsfastyet.com/

Particularly watch the video from velocity linked at the end of the page (and the slides). There is a ton of tuning that needs to be done to eliminate round trips from the TLS times.

If you look at the bottom of the waterfall there is a bandwidth utilization chart and while it does eventually ramp up and saturate the link there is a lot of dead time at the beginning that can be tuned.

As GreenGecko mentions, you'll also want to move the JQuery UI code to your server.