I love this site, and have been using it extensively over the last week.
Any chance that South Africa can be added as a test location?
Or any tips on how to test page load speed for South African users?
Sure, have a spare machine lying around? 
Most of the locations are run by partners, I only run the machines in Dulles. I’d love for someone to volunteer some equipment in South Africa for a test node: http://www.webperformancecentral.com/wiki/WebPagetest/Hosting_a_Test_Location
If you don’t want to go quite that far you can also set up a private instance on a machine and do your own testing: http://www.webpagetest.org/forums/showthread.php?tid=375
South Africa is here now, on Azure. However I noticed that (as of a few days ago, at least) if you’re using Azure CDN from Microsoft with an Azure VM, requests for the closest Anycast node are being routed to Europe, not South Africa (see “Update 2” in that link). This results in requests to CDN endpoints taking ~200ms (if cached), rather than ~20ms. Worth bearing in mind if you use them.
The dotcom-tools.com test node appears to be hosted elsewhere and ironically does hit a local Microsoft CDN node.
This should not be confused with old IP Geolocation databases not reflecting that Azure VM IP range is in South Africa, although that is also an issue (and perhaps is part of why the IP routing is as it is).
It should also not be confused with the main issue at the above page: misses from South Africa edge nodes going to Europe and then being requested from there - which is probably the right choice if your CDN origin is in Europe, but not if it’s in South Africa as well.
In short: if you’re trying to get high performance in South Africa, testing is key - and you should probably try multiple test providers.
If you’re trying to test for South Africa, Fastorslow.com has that location (And 17 others) we use it in tandem with this awesome tool and it offers all of the information that we need to troubleshoot any performance issues.