I see, its quite hectic and you will find people with good ideas but might not be the best for your taste.
from what I see you got your basics and balance in order, and all you want is just a small increase to future proof. When I it really make saw the thread name of "more FPS" it makes you sound like an enthusiast rather than a mild mannered citizen of the master race.
The guys who are ask/tell/suggest -ing you to go haswell or newer are actually thinking that your specs are dated, and to ensure FPS (enthusiast in mind) then you should go balls to the wall and upgrade (especially when now we know you're not the second hand parts guy).
I do the usual how do I see my rig in 3 years time, right now my haswell is worth something so I can sell and buy newer things. But your FX 8350 is quite dated in our minds and the price will be low if you want to trade up. Your R9 200 series is also dated cause in my mind the AMD R9 300 series are the border betweeen still ok and ye olde parts beware.
If the Mobo Doesn't accept any RX series, try contacting MSI and ask for a BIOS update. I remembered My first build of MSI K9A Platinum with PCI-e 1.1 slot, Bought me a 5770 with great personal expense and distraught due to the mobo not working with it (5770 requires PICI-e 2.0). I thought it was the PSU, and traded up 2 times (Corsair VS 450-Corsair VS 650-Corsair TX 850), I didn't know the problem was my bios and slot, and it broke me everytime my PC just wont POST. My friend asked me to write MSI a letter, sent the email in the morning got my reply in the afternoon with a BIOS update, and I never forget to check BIOS updates ever since.
I got an ultrawide monitor, cheap one with 2560x1080 25 inches of fun, I get to see half a Dota lane and a larger field of view in CS-GO. It gave me the edge to get the best results my skills can produce, but that resolution comes at a price.
In the end, please decide what you want to do but get the whole story and options before execution, I want My money to get me the best and I think I got it, In FUN we TRUST!