Is my PC performing as expected / should I upgrade?

Hi all.

Recently I got a Sapphire Nitro RX480 to replace an old and underpowered card. However I'm not quite getting the results I was expecting, especially compared to game benchmarks from various sites. Unfortunately I cannot find the links (I'm at work) however an example would be that GTA 5 would get between 70 to 80 fps on the in-game benchmark with the same card, I am getting 40 - 50 fps on exactly the same settings.

Setup.(PC)

AMD Athlon X4 760K On a Cooler master TX3
Crucial Ballistix DDR3 1600MHz dual channel.
Corsair CX 500
MSI MA75 P33 FM2
Sapphire RX 480 Nitro+ 4GB (1350 core 1750 memory)
3 SSD ' s

I ran Valley a few times.
High settings DX11 1920x1080 full screen AA off
and here are the scores:

With the CPU at 3.4GHz (Had issues with cooling, added new fans so this was my previous under clock)
1980 AVG FPS 55

With CPU at "stock"
2272 AVG FPS 59.7

With CPU at 4.0GHz
2540 AVG FPS 61.4

With CPU at 4.2 (Not stable).
2754 AVG FPS 65.8

So what I would like to know is, its the GPU working okay, if not I can still send it back but I need to find this out.
Does it make sense that my CPU is slowing the card down this much.
Is it worth spending money to upgrade to a new platform? or get a decent MOBO and cooler to overclock if the scores are looking close to how it should perform.

As a reference, my friends 8350 + 7870 XT gets 2134 on the same benchmark.

When I get home I can post images of the scores and the Wattman graph as someone might be able to tell if something strange is going on.

Thanks.

CPU is holding it back. Here you can see just how much of a difference the CPU will make in games that are somewhat CPU intensive.

Thanks, it puts it into perspective I guess.

Any recommendations for a new CPU? Looking at a 6600K or 4690K which are strangely the same price at the moment.

Would anyone know what real world benefit I would see from this? (I don't know anyone with a recent intel build so I cant just go round with my card and see) I keep getting mixed results from benchmarks.

Yeah, the Athlon X4 760K isn't all that powerful unfortunately and with an RX 480 you're looking at roughly GTX 980 level of GPU horsepower.
See here for stock for stock comparison of the Athlon X4 760K and i5-6600K. It's not all that impressive game list but gives you a hint about the big picture..
Scroll all the way down for game benchmarks done on a GTX 980, the difference is quite staggering in some cases.
http://www.anandtech.com/bench/product/1686?vs=1544

I would personally go for a Skylake based system if you're building new. If used then go Haswell.

Skylake would of course mean you would need new RAM as Skylake is DDR4.
Although yes, Skylake's memory controller does support DDR3L as well but the DDR3 motherboards (or DDR3+DDR4) aren't all that common and you would still need to buy new RAM as your Crucial memory probably isn't DDR3L.

Out of 300 or so LGA1151 motherboards out there, there's 64 motherboards that I know of which either have DDR3 or DDR3+DDR4 support.
Out of those 64 there's just seven (7) motherboard with the Z170 chipset, these are 4x DDR3 boards.
http://geizhals.eu/?cat=mbp4_1151&xf=317_Z170~493_4x+DDR3+DIMM~493_4x+DDR3L+DIMM#xf_top
If you want 2xDDR3+2xDDR4 board you'd be limited to a whopping number of three different boards from either Asrock or Biostar with either H110, B150 or H170 chipset.
http://geizhals.eu/?cat=mbp4_1151&xf=493_2x+DDR4+DIMM+%2B+2x+DDR3+DIMM#xf_top

CPU? i5-6600K or i7-6700K if you wish to overclock.
Even an i3-6100 (2C4T 3.7Ghz) would be a big boost for you, here's the i3-6100TE at 3.645Ghz compared to the Athlon X4 760K.
http://www.anandtech.com/bench/product/1686?vs=1645
The i3-6100TE running at 3.645Ghz isn't a perfect representation of the i3-6100 performance which is clocked at 3.7Ghz since the TE version is a little bit different and has more L3 cache (4MB vs 3MB) but it shouldn't make a huge difference.

Aaaand switching the Athlon for the i5-6600K, the comparison looks like this
http://www.anandtech.com/bench/product/1544?vs=1645
Not a HUGE difference so if you are tight on money, you can certainly get away with Skylake i3 and spend more money for nicer motherboard, more RAM or say m.2 NVMe SSD or something.

Though of course if you do other things with your computer, say video editing or rendering or Twitch/whatever streaming or something like that which scales nicely across multiple threads > an i5 or i7 will be much better choice than the i3.
Especially an i7 if you're streaming and playing a CPU intensive game at the same time.

Thanks for the reply it helps. I'd probably go for an i5. Realistically is there much performance difference between the Intel chipsets? I will only be getting a K part if its on offer.

There are no differences in performance between chipsets of the same generation. The differences are in features.
If you want to overclock, you need a Z chipset as it's the only chipset that is officially supported by Intel for overclocking. As well as a K SKU.
For a quick comparison between the chipsets, here's Skylake or LGA1151 socket

And here's Haswell for LGA1150 socket