Installed the 310s last night and lost about 5-8 fps in Prepar3d. Did some tweaking in Nvidia inspector and could never hit a "sweet spot". So I rolled back to the 306.97.
Using MSI GTX 670 OC here with I7-3770k@4.6ghz and Windows 8.
Win 8 here working fine with FSX, Have spent the last few evenings working on Prepar3d in Win8. Have GEX, UTX, REXe+Overdrive and FacetrackIR working well in Prepar3d on Win 8. It really looks great!