Eliminate render-blocking JavaScript and CSS in above-the-fold content

Hi,
So, I'm trying to speed up my website load time.

I've got Hummingbird, and it's telling my biggest problem is image size, which I'm trying to fix with Smush Pro. I've open another ticked on that question.

But I've also done speed tests in two different sites.

The first is Google Page Speed Insights. Google says for desktop I should address image size, and for both mobile and desktop, I should "Eliminate render-blocking JavaScript and CSS in above-the-fold content"

The second test I'm running is a site at tools.pingdom.com
They say I need to do the following:
1. Combine External Javascript (does this fall under "Eliminate render-blocking JavaScript and CSS in above-the-fold content"
2. Parallelize downloads across Hostnames
3. Combine External CSS
4. Specify a Vary: Accept-Encoding Header
5. Remove Query Strings from Static Resources

So does Hummingbird, or any other WPMUDev plugin doe these?

It baffles me that I have to worry about this - seems WP would optimize these things form already to make it so that my site loaded as quickly as possible.

I'm still getting load times of more than 5 seconds - unacceptable as I see my visitors bouncing when the page does not load immediately.

Thanks, for your help!