You can edit the processor model and topology in virt-manager. If you don't emulate a different family of processors, you won't lose performance. You can however emulate any processor you like. If you don't emulate another family of processors, you just change the processor topology to 8-core, it will work just fine.
No CLI is required, you can do everything in the virt-manager GUI.
fps is 10-30 % higher in a linux-hosted kvm windows guest than on a bare metal machine with the same hardware. That is with PCI or VGA passthrough. There are almost no games that take an fps punishment, but it can happen. Some games have a much greater boost in performance, depending on the distro and the general system configuration. To have more performance, you have to keep your linux install as clean as possible, no closed source crap, no skype (works better on a phone anyway), no flash (html5 uses much less resources and has better quality and no DRM in linux, whereas Adobe flash player introduces DRM in linux), etc... just no shortcuts but conscious system configuration, netfilters up, SELinux enforcing, only official license-free and pure FOSS repos (except maybe for some "bad" codecs from an official repo), just everything shut tight for maximum hygiene, a good repo (nothing Ubuntu based, best to stick to Gentoo, Arch or Fedora, or Debian or Slackware if you don't like modern kernels and don't mind solving problems that exist only out of principle). Discipline pays off, keep your system clean and the sky is the limit, step in a honey trap and you're screwed, it's as simple as that.
Simcity and COD both run in wine, you don't even need windows for that. You'll need Windows dll's and some wine config tinkering, but when it's configured right, CoD4 and 5 gain about 10-15 % of fps in wine in comparison to a bare metal windows install, which is about the same as the fps gain you get in a VGA passthrough kvm container with those games. Neither CoD nor Simcity are heavy on the system requirements, they should both run very smooth with wine.
Thing is, with linux you just can't go wrong. Microsoft is the third largest linux support ticket seller on the face of the planet, even though they don't have any linux-staff, they just resell Novell SLES support tickets to their customers with a 50% price premium. In fact, you might say that Microsoft finances SLES, per year they sell about 300 million dollars worth of support tickets for Novell. In return, Microsoft asks of Novell that they accept that the fact that linux is FAT/NTFS compatible, means that linux is licensed from Microsoft, which is of course pure bullshit, but with mega-stupid and corrupt judges like the Apple-judge Koh and mega-dumb and corrupt civil servants like that Microsoft-woman that is in charge of Obama's anti-trust policy, Microsoft has a very good chance to pull it off anyways, look at the 2 billion dollars of license fees Microsoft receives from Android phone manufacturers for the use of the FAT filesystem, which they need to use, not for any technical reason, but simply because the US government forces them to use it, so that they can incorporate DRM, which makes use of Flash and Microsoft filesystems, both of which are archaic and extremely broken and unsafe technologies, and for that, 10-20 % of the manufacturing price of a phone goes to Microsoft... so the further you stay away from Microsoft and affiliates, and keep your system clean of open source, the more you benefit on all fronts. Sometimes that means sacrificing some user pseudo-comfort, like having to jump through some hoops to get games to work, but it's not like every game works out of the box on a MS-malware system, and often making "Made for Windows" games work on Windows is harder than making those games work on linux...
I can only give one advice to anyone that is serious about computing: talk to people, go on open source fora, post questions, send messages to devs or FOSS-support people, don't be afraid, the FOSS community is not XBox Live, 4Chan, YouTube or Google+, you won't be flamed for nothing. Learn linux by social interaction, linux and open source was and still is community developed thanks to the internet, without the communication channels provided by the internet, it simply would never have existed. So if you want to run a game in wine bout don't know how, hit winehq on the net and ask around. I'm not the biggest gaming specialist, I'm not the biggest gamer, and IF I play games, that's mostly FOSS games that are linux-native or pure cross-platform, so I can't give many specific hints on making specific windows-games work on linux with wine on specific hardware combinations, I don't even have wine installed on most of my systems. But the guys at winehq, crossover and winetricks know everything there is to know and can probably give you the best configuration for your games on your system.