I'd love to hear the criteria for why you prefer Avid Express to Vegas. I've also used both, and I can think of several reasons right now why Vegas is superior to Avid Express. If fact, I could extend this to FCP as well. Anyway...
Let's be honest. The fact that you've quoted the standard MAC talking points like "don't give into Mhz myth" and "They can do everything your PC can do (except maybe gaming)", means to me that you simply prefer MACs and you haven't seriously evaluated PCs. Current PCs are fast, reliable and overwhelmingly dominant in the home computer arena, so it won't fly to simply to declare Macs are better without actual proof. I can respect that you prefer MACs, but this discussion is about why a PC-based video editor should go through the bother of switching platforms.
FCP was once the top desktop NLE sofware. However, FCP is no longer demonstrably superior to the desktop NLE choices available for PC. The comparitive reviews I've read don't support this. Perhaps you could provide a review for us to study.
PC users know that Windows is just as reliable as any current MAC OS. That argument resides only on MAC user forums. We're way past that since we use Windows every day. The amount of available software titles for PC simply dwarfs those available for MAC. Almost all the 'high-end' MAC software (Apple software being a notable exception) is now cross-platform. A MAC may be able to run MS Office Apps in emulation, but it couldn't run high demand, real-time editing software like Vegas that way.
It seems to me that for video editing, there's every reason for MAC users to switch to PC, but no real reason for PC users to incur the expense and learning curve of switching to MAC.