Is this needed for AMD based machines

You can run the Phoronix test suite before and after enabling them. There's not a lot of data on the various recent AMD platforms, presumably because of the smaller market share especially until recently. I imagine there's a large difference between mitigations=on and mitigations=off on the pre-Zen AMD platforms and a smaller difference between the two on the most recent AMD generation.

I can't find big difference between iPhone 6 and 6S.

Yeah, the moral of this story was "Well, there goes one reason to upgrade"

I have done R&D to find Django CMS and e-commerce like OpenCart and I spotted Wagtail but I felt it's still growing and didn't reach the level Wordpress. PHP web apps are mature than Django Apps and we need to support this.

Please give me guideline on who to contribute or even how to use it and I'll do my best to help.

Contributing - there's a big list of Github issues you can help with:

https://github.com/torchbox/wagtail/issues

How to use it - the docs are pretty comprehensive:

http://docs.wagtail.io/en/v0.8.6/

Getting help - join the user group:

https://groups.google.com/forum/#!forum/wagtail