We're working on a refresh of the technology preview. Very interested in your feedback on this issue once it's released.
I can see the same issue now with the July version and I didn't had the issue with the May one ...
I turned off the accelerate 3D graphics too and everything is back to normal ...
I'm using a macbook pro retina 15 late 2013 with a Windows 8.1 x64 as a guest ...
The July version is still very laggy when using Office applications
15" MBP Retina, Scaled Retina(+1 resolution), Windows 8.1 SP1, Office 2013