X51 R2 Upgrade: PNY GTX 960 4GB vs. EVGA GTX 970 SC

I just got my 330w power adapter and I'm ready to upgrade from my OEM GTX 645. The 960 seems to play most games out there at close to 60 FPS at pretty good settings. Obviously the 970 is better. It seems to me that the 960 is much more stable. Would love to hear what you guys think. I've read a lot on here about people putting 980s in their X51 R2 but before spending over $300 on a 970 I'd like to get a bit more feedback. I'm going to purchase an Asus 144 hz monitor in the near future as well and I am seriously concerned about how a 960 will work with a monitor like that so I'm leaning towards the 970. But, man, after shelling out the money for the 330w power supply, getting a graphics card and a nice monitor I'm not sure I want to be in a position in a few months where I'll have to finance transplanting my X51 to a new case and getting a new PSU because the 970 OC is too much for the small X51 case.

Any feedback is appreciated. Thanks.