Guys I am not trying to be a turd burgler or anything and YES I am a VMware zealot (but take it from a man who came into virtualization from LPARS/Xen/openvz (proxmox has this container tech and KVM for full virt), and KVM)...I danced the open source Virt gammat and once I crossed over into the Enterprise space and saw the mgmt and extremely forward thinking ideas and brilliance coming out of Vmware eng I was astonished and somewhat saddened that the open source community could not keep pace...then again VMware had a good 6-8 yr jump/headstart on everyone in x86-land when it came to virtualization.
Long story short and getting back to my point...if you're waiting on drivers for new HW I can almost assure you 95% of the time Vmware will beat OS, open source, and other vendors to the punch so again just have a lil' patience I would not be one bit surprised if I start to hear chatter about 10G support for this platform start coming out of the Vmware/virt community woodwork.
Ohh btw, very curious, you said 10G works in Win2008 or 2012 (I forget which, doesn't matter to me), does that same adapter show up as a usable adapter to pin vSwitch (if that is what Hyper-V even calls it, prolly so) traffic to? Would be a bummer if at OS Win level it worked but Hyper-V it didn't...can't imagine why but would never put it past M$. :-D