Created attachment 214905 [details]
here is an example of the artefacts. they go away after the slow down stops, which can be anywhere between 0 and 5 seconds.

I've just made a switch from 2.6 to 2.8 and immediately I notice while holding space or middle click to scroll over the image a horrific slow down and artefacts where the program wasn't drawing in sync.
The slow down almost makes it unbearable to use the program at times freezing for 2 seconds before updating.
if its at all relevant I am running on 64-bit windows 7 with no-fonts on because the startup crashes when it tries to load fonts.