Thanks, I bought a Z97 Deluxe a few days ago and had the very same Wifi related freezes. Turning off all ASPM related options fixed the problem. As I later found out, you can leave everything turned on except of "Native ASPM" under Platform Misc Configuration, which lets the BIOS control the power management instead of leaving it to Windows.
Thanks again, I already thought I had a broken mainboard and wanted to return it.