Upgraded to Yosemite on MBPr, WiFi is painfully slow

I got my MBPr 15" last year, and for a while I was using it as a laptop. No issues.

I then got a bluetooth mouse & keyboard and the issues started. I found this monster thread, with lots of people having similar issues:

https://discussions.apple.com/thread/5495375

TL;DR

WiFi doesn't connect after waking from sleep, and the WiFi is painfully slow for no reason

After repeated conversations with Apple, and trying every "fix" I can find online, it randomly just started working again. Apple repeatedly told me it was my home network, despite all my other devices (Android Phone/Tablet, Windows Laptop, PS4 and Chromecast) being completely fine in the same location.

To give you an idea of the issue, my other devices were getting about 38Mb down, and the MBPr struggled to get to 1Mb down (even though the upload speed was fine - something like 7Mb)

The issue went away and I was happy. I've just "upgraded" my MBPr to Yosemite and straight away the issue is back. This is not an issue with my home network. It happens on different networks too!

I've tried deleting the network preferences, bluetooth settings and resetting the PRAM. Nothing is working.

Seriously Apple, sort it out and stop placing the blame on your users. We are no holding it wrong or whatever excuse you want to use.

In the mean time, has anyone else found a fix for this...