Unfortunately, your nice 12 core processor is being severely wasted on Sins, but 3.7ghz should be more than enough to avoid what you're running into. It is not a memory issue, that leads to a dump, not a hard freeze requiring a reboot.
That it freezes when you zoom in implies it's a problem with your graphics setup, something is hosing pretty majorly when textures are being utilized by your graphics card. You still shouldn't have to reboot, it's just locking up your graphics driver so you can't see task manager come up, window mode should solve this.
I'd do a graphics driver update, check directx while you're at it, and then play in window mode until you've fixed the problem. An R9 260 shouldn't even be worked running Sins, so it's probably just a bad driver and not a bad card that flips out when it gets taxed. The other possibility is that Sins is actually being run on your Kaveri instead of your R9. Possibly both, I'm not familiar enough with the setup. Either situation could result in performance issues though.
You can also try disabling auto-record and auto-save as well, should they be enabled.