Is the R9 270 still good enough or is it time to upgrade to another card? Most games I see it seems to run everything on Ultra but now there are a few like Witcher 3 which seem to only let it run on medium.
Main question is how badly you need new GPU, if you can wait few months wait for GPUs on 16/14nm node 2x more performance per watt
If you want go earlier try look for local deals and second hand offer ebay ect. you can get cheap R9 280/7970 R9 285/ R9 290
With that graphic card you will run witcher 3 on medium or high if running at 1366x768 , you should upgrade since you can get a better graphic card at cheap price , what is youre cpu?
Main question is how badly you need new GPU, if you can wait few months wait for GPUs on 16/14nm node 2x more performance per watt
If you want go earlier try look for local deals and second hand offer ebay ect. you can get cheap R9 280/7970 R9 285/ R9 290
You will no need new mobo for new GPU 😉
PCIE slots are standard and they will still be in use, but for how long who knows but for sure for next 2-3 years