Only thing I can tell you , and been repeatedly said over these forums is, your R9 will get bottlenecked by the CPU as compared to other processors performance IN the exact same system, exact same setup, exact same game. The best performer is the i7, then below that is i5/AMD9xxx-8xxx, then rest of AMD/i3s
http://www.bf4blog.com/battlefield-4-retail-gpu-cpu-benchmarks/
On iCores, you need to pay attention to the -xxxx after it because of the different generations would perform less then the previous generation. As noted when going 'top tier' gamecard the i3 bottlenecks more then the i5 (naturally) when comparing results, though you just watch the new i3 Haswell on Ultra perform like a champ (WOW! STILL!)
http://www.imagelucidity.com/news.php?id_2=1050&?topic=Haswell-Showdown
I know you probably heard 'get the best game card possible because games only use GPUs', this is false because the GPU does not read data directly from the HDD. Your game is stored on the HDD as code, the RAM reads a 'clump' at a time from the HDD to pass to the CPU, the CPU then processes as to what it is and what component needs to 'do with it' (print it, render a jeep, post to Toms Hardware, etc.) before the GPU even gets involed. So a slow HDD (5400RPM) or old RAM (some people still on DDR2) or a lower end CPU will all 'bottleneck' the performance the GPU 'could be performing at' if it wasn't twiddling it's thumbs waiting on the 'slower' other part to get the data to it.
Oh and that isn't considering how much BF4 and some other games are 'CPU HOGs' using the CPU in-game as much as the GPU is used to 'render it' (many many many links talk about this new change in 'nexgen' games).