Gaming with AMD Radeon R9 M370X on Parallels?

You will not get good performance on any VM engine.

I actually am gaming on my OLD MBP mid 2010. I've installed Windows 8.1 using boot camp but am also able to boot into the partition using Parallels. In other words, the Parallels is not having its own files for Windows on my OSX partition but boots the other partition while I'm in Yosemite. To be honest with you, it's really good to game in bootcamp as you just need to restart the laptop and boot into the other OS and is very very very fast to do so if you have SSD (which you will); you'll be able to change the OS in less than 15 seconds. With bootcamp, you'll get better result with I would use when I'm playing hard or am not using anything in OSX. but sometimes, you're using an app that is on OSX, so you'll stay in there and use parallels. both ways work, but you'll experience better using normal boot. Parallels was actually the first VM I loved; it's very smooth, fast, reliable, and can boot the OS you already have on the other partition which is very good to save space on the SSD. hope I'd helped

Both Parallels and Boot Camp are very well made for what they are made for. Let me tell you this, Windows is not able to read/write into/from the OSX partitions, but both Parallels and Bootcamp solve the issue. So after you install Windows using bootcamp, you can see the OSX partition is added to your "This PC" (New My Computer). so you can save a file on OSX, then access or even edit it on Windows when you're completely in Windows and are not running it in VM. same goes the other way as OSX can access NTFS but is not able to write into it however. (you can just access the file from windows so there is no point either).

Parallels in other hand, makes a virtual HDD for OSX when you run your windows in it. files are updated constantly there. so for example when you can make an Excel file in Microsoft Office on OSX and save it into the desktop of your windows using that virtual HDD (which has the paths of your Windows partition) and then just bring the Windows window up and open it (or edit it) there with Microsoft Office on your Windows.

Parallels can make the Windows full screen in another desktop (you get what I mean if you're familiar with OSX, as you can have multiple desktops on a display). switching between desktops is just moving 4 fingers from left to right or right to left on the touchpad. this way, you'll have both OSes and can switch very fast in 1 second. However, more RAM is obviously better to make hem run smoother side by side; I had 4GB and it sometimes was not very smooth but now it is with 8Gigs. Other good thing with parallels is you can copy in one OS and paste in another (text and bare images, not files) (for files use the virtual HDD); you can use mac shortcuts on windows like Cmd+C for copy and so on (and Control+C also works well so you can have yourself used to one or both); and also three finger dragging witch is a very good option on macs and windows PCs really need them, so you can have it on windows. (Google this feature, you'll love it)

About the games I played with no problem on VM (and remember my mac is really old, 2010): Driver San Francisco on mid settings, WARP mid settings, Rise Of Nations, Sims 3 low settings

And normal booted Windows (not VM): Driver San Francisco on ultra settings, WARP ultra settings, Rise Of Nations, Sims 3 high settings, Euro Truck Simulator high settings, Call Of Duty MW2 mid to high settings.