Thanks for the chance to use this preview version, I'm always happy to test new apps.
I have upgraded my Win 8.1 x64 virtual machine to the new Tech Preview, and continue to use it as usual.
However, I have to say that the virtual machine gets way too lagged on a Excel 2013 spreadsheet, I have already checked for the "Troubleshooting" settings of the virtual machine and turned them to None (it was on default setting) and I still notice severe lag on Excel.
That's my report, if you need more data just ask me.
Do you have the "Disable graphics acceleration in the Advanced Options" checked?