No matter what my budget is, I always try to spend good money on my PSU. I've had a whole system become useless because of one bad PSU. My recommendation is save some money and buy a nice semi-modular one.
Nvidia's naming sequence can sometimes throw people off but I'm glad it worked in the end for you. More than a 50% increase in performance. That should keep her happy for a while.
Get a used 290x for 300.
Edit: Nvm, just realized that gtx 970 runs as well as a 290x. In that case, I agree with everyone and say you should get a new gtx 970 or buy another 270x for CF if you're on a budget.
I heard these cards weren't really worth it. Anything lower than the 270 performed really poorly when it came to games. The r9 270 is too cheap to pass up as well.
I would say its worth it. Games are becoming a lot more graphically demanding and if you have a 1440p display, it'll run pretty much anything at that resolution with a smooth 60+ fps.
AMD cards tend to run hotter than their nvidia counterpart. I have a r9 270 that's heavily overclocked and it hits the same temps as you under full load. I've even had cards than ran at 90 degrees just fine.
No, I dont think it's overkill. Newer games are going to require a lot more powerful GPUs soon. Keep what you have man, there's no such thing as overkill for us PC gamers :)