I just worked out another reason to use .com.au for aussie websites, instead of .com (I see that question now and again).
The .com site has another 0.3-0.6 seconds DNS lookup time, before the web page even starts to load.
I have a few customer’s sites I am accelerating, but still suffering slow DNS times. So I plunged into some network observing.
If you want the technical why … the .com DNS servers are mostly in the US, 1 of the 12 or so .com DNS servers are picked randomly, and asked where blahblah.com is. Even if the WordPress website is hosted in Aussie, the first DNS lookup has to go to the US and back in order to find where your DNS server is.
If you’re DNS server is in the US, there is another bunch of time for the next DNS query.
There is a few DNS queries, not just 1:
So even if you have your hosting here in Australia, and your DNS server is here in Australia, and your failover DNS server is here in Australia, but you have a .com domain name, you’re getting taxed 300ms (0.3 seconds) on the initial page load.By Scott Farrell on May 5th, 2016