Yep, I also have Office for Mac installed. I use Lync DAILY - I host a daily Lync meeting with developers all over the world. It's great for collaborating and screen sharing. The times I do want to share video, yes, like you, I'll use the Mac client. And like you, I have the same experience during screen share the CPU spikes and the fan kicks in. Also, on OS X Lync, you can't give someone control over your screen like you can in Windows. So, I would MUCH rather use the Windows version of Lync 2013. One more thing about Lync - the iOS Apps are REALLY weak. Anyway, enough about Lync - I can go on all day about it.
The main issue is the FaceTime (aka iSight) camera doesn't work under Fusion. I had a tough time even getting the drivers to not show a Yellow driver missing icon in device manager. I ended up finding a hacked .msi file here: https://discussions.apple.com/thread/4104426.
Once I got rid of the yellow alert in device manager, I thought it would all just work, but in Skype for Windows and Lync for Windows, the video just freezes. I've been "suffering" with this since August when I first installed Windows 8!
Today after looking AGAIN at trying to get it work, and seeing a friend running Parallels with no issues, I just switched to Parallels!
Parallels imported my Fusion guest OS no problem, and it's running even BETTER than Fusion. I just re-ran the Windows Performance Assesment and I now have 8.2 HD, and 7.9 RAM scores, which are higher than Fusion.
And of course, the camera is working - flawlessly. Already had a 30 minute Lync call with no issues.
Done. Fusion out. Parallels in.
p.s. I wonder if this post will be deleted.