DX10 support in recent versions of PD8 is good.
It's all relative. If Bootcamp was giving a 100% improvement when comparing 30fps to 15fps that is one thing, but if it is 120fps compared to 60fps, it's largely irrelevant.
You keep on mentioning 'not too demanding', but I have already stated that I have had good experiences with Skyrim, F1 2012, Deus Ex HR and The Witcher 2 on PD8.
What you are calling "good experiences" is subjective. Your idea of a good experience and mine could easily be very different.
The benchmarks for Parallels 8 with DX10, including the ones I ran myself with 3DMark Pro, were awful. The performance in this first iteration of it has a long way to go. I don't think they should have even released it yet it was so bad. And again, there is no DX11 support at all.
I think I understand what you are saying despite all that. You are okay with less eye candy at native resolution and plenty of games run well enough, with sufficient frame rates to be okay with you. As I said earlier, that is fine too but to dismiss a 50% reduction in performance as if it should be irrelevant for the rest of the world is something I am questioning.
See, my point of view is that I paid damned good money for this hardware and I'm not content to play something like Skyrim with anything less than the maximum settings this hardware can deliver. I can crank those settings up higher in native Windows 7 than you can running it in a virtual machine. There is just no getting around that.
Anyway, it is perfectly fine for you to make the tradeoff that you do when you are happy with it. I am not critical of that. By the same token I think you should be able to appreciate why someone would want the maximal performance their hardware is capable of.
Another issue with running in a virtual machine that can occur is video display issues since the emulated video adapter relies on some Wine technology I believe. I forget where I read that now. I am thinking it must though since it needs to translate DirectX calls to OpenGL calls in OS X. So, you can encounter cases where a game does not display correctly in a virtual machine whereas it works fine with native Windows.
Here are a couple examples of what I am talking about and these are older games to boot:
Halo: Combat Evolved: I ran this in an XP SP3 virtual machine and the display of regenerating shields was corrupted. I then ported it with Wineskin and observed the same corruption. In native Windows, it displayed fine.
Halo 2 (the first DirectX 10 game I believe): I ran this in a Windows 7 virtual machine and the display stuttered as the performance was so bad. This game is a 2007 re-release of a 1st gen XBox game! The problem? DirectX 10 support in Parallels 8 leaves a lot to be desired. I'm am hopeful it will improve in time but it is not currently useful if it cannot even manage Halo 2. I run the same game in Windows 7 natively on this hardware at max settings and the game runs smooth as silk start to finish. Huge difference.
So it is not all a bed of roses trying to run even older games in virtual machines, never mind new ones.
For a newer and demanding game example how about Hard Reset? It is not playable in a virtual machine running Windows 7. It stutters constantly. This is a beautiful game loaded with eye candy but you cannot enjoy it in Parallels. However, run in native Windows 7 at high settings on the same hardware, it runs smooth as silk.
Those are some recent experiences I have experienced first hand. It's like Wine. Some stuff will work well, some stuff won't work well at all. However, i am not blaming Wine for these performance issues. It is the VM overhead that is causing them.
For a game like Black OPS II where you want a stable 60 FPS for competitive multiplayer and the best visuals your hardware is capable of (well, I do at least), this is not achievable running in a virtual machine.
I do think for some games, having the VM option is great as it spares you reboots and there is compromise you can live with or even not notice as you pointed out for some cases. I am certainly not knocking Parallels. I own Parallels 8 too and it is very handy sometimes for a variety of purposes. But it cannot run every Windows title I still own acceptably or at all in some cases.