I am facing NO problems with windows 8.1 64bit, in neither of my 2 workstations and 1 laptop!
The 2 workstations: i5 - ati 777 and i7 nvidia N650. Laptop i7, nvidia 740M.
Only issue, but not verified yet, is when i ran the client at FULL graphics, i ended up crashing twice, so i reuced the lvl of detail.
I havent double checked yet though!