If you changed from the 750ti to the r9 290 to play Minecraft that wasn't a smart move...
R9 series are focused on 4K and VR, therefore they have a high bandwidth and memory, but it has a low core and memory clock.
750ti has a lower bandwidth and memory, cause it's not meant to play games at 4K, but it has a higher core and memory clock, which are the numbers that will make more difference in your the performance of your Minecraft.
What I'm saying is that you're not using the r9 290 the way it was supposed to be.
I'm pretty sure you're not playing at 4K, or the r9 would probably have the best performance