syrphic :
i have a AMD A10-6800K Quad Core 4.1GHz FM2 4MB Cache 100W TDP CPU Processor
I would look at a GTX 760 or an AMD r9 280 or r9 285(when available). Anything higher will most likely bottleneck because of your APU and be a waste of money.
Is your case m-atx as well, or are you just running an M-atx board in a mid tower case? If it's a micro atx case you will most likely need a low profile card as well.