or would it be better for me just to upgrade my graphics card since mine is 6 years old instead of paying hundreds for a new system?

The motherboard is Asus P8Z77-V LX if that helps

I'm still very happy with my 3570K. You can easily overclock it for free performance if you want an upgrade.

You can use any card you want, but post your power supply's model number. You may need a new one.

You also didn't post your storage, but it's 2018 and you need to have an SSD.

931GB Seagate ST1000DM003-9YN162 (SATA)
OCZ StealthXstream 2 600W PSU

So yeah, sounds like you don't have an SSD. Definitely buy one. 240-256GB minimum, but I'd recommend the 500GB Samsung 860 EVO, it's a stupid good value right now- just bought one myself.

The 3570k is still a solid chip, it'll easily still manage so while you'd see a benefit with a CPU upgrade, it's absolutely not necessary. I'd hold on to the CPU and Mobo for now, overclock it a bit though. I'd also add another 8GB RAM, DDR3 is cheap as chips these days anyway, can get 8GB for £20-25 ez.

I'd upgrade PSU to a good quality, modular 550-650W unit. EVGA G2/G3, SaeSonic Focus, Corsair RMx, and Bitfenix Whisper M are usually well priced and all good quality.

You could upgrade case if you wanted, you can get some really good cases well under 100 quid these days, but if your current case does the job and you don't mind it, might as well keep it and save the money.

I'd definitely upgrade that GPU but I'd want to know what monitor you're using first because you might want to consider a monitor upgrade which would very likely be a better investment than a CPU upgrade, so another reason to hold on to that 3570k potentially.

Would also be useful to know what you're using your system for exactly.

more details

Asus P8Z77-V LX Motherboard
sound: onboard
Chillblast Vantage Black Midi Mesh Gaming Case
Nero 3 CPU cooler with Artic Silver premium thermal paste
Monitor- Samsung about 19 or 20 inch, max resolution it supports is 1600x900, can't remember the price but it was a cheap one

I got the computer from chillblast, they let you choose the parts you want from a selection.

I originally intended to overclock it (hence the 3rd party cooler and paste) but put it off after reading scare stories online about things going wrong.

I listen to a lot of music, look at a lot of porn, play some games but nothing too heavy.

Would I notice a sound improvement if I bought a sound card or is the onboard sound good enough? Would the current PSU be good enough if I just upgraded the video card and storage?

Time for a new monitor.

I don't believe in sound cards because the inside of a computer is a bad place for audio hardware and you can get better quality with a USB DAC and amp. Whether there will be an improvement depends on your speakers and headphones.

As r00t said, monitor upgrade would be a good shout. I'd look at going 1440p, or ultrawide, maybe even 4k.

I'd also agree that a sound card would be pretty useless. Your motherboard audio is going to do about as good a job as a sound card IMO, if you want to improve audio then you'd be better off looking at external solutions, as opposed to internal.

That case is trash. Easily re-usable if you don't care though, so entirely up to you if you want a case upgrade. The PSU is pretty old and I'm not sure about quality. It would likely be fine with a GPU upgrade, but I'd recommend replacing it with something newer and better quality, you have the budget for it anyway.

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What games do you play?
For monitor, would you prefer ultrawide, high resolution, or high refresh rate?
Would you want a case upgrade?

I thought it was a good case because it's spacious and has a side grill for ventilation? I'm not too bothered though.

How much would I need to pay for good quality speakers? I bought £30 hp ones from a supermarket and I would say they are satisfactory but nothing special.

I've monitored my RAM usage and I don't think I would ever go above using 5GB at once. That gives me at least 3GB free RAM at all times.

I think I can narrow my upgrade needs down to a new monitor, new video card and possibly a PSU.

I don't want a wide monitor just a good quality image that makes pics and videos look good.

The most intense game I play is "Ultimate Epic Battle Simulator" this game can involve very large numbers of battle units in the game at one time (you can choose how many). I would like a video card that can support very large numbers of units. Or would this be the CPU's job? Is the video card's job just to display the images?

I also play minecraft and would like a video card that would render quickly and let me see far into the distance.

oh and I like to use the foldinghome project that let's you use processing power to help with projects. Apparently I can't use my video card for this because it doesn't support double precision calculations.

buildafire wrote I thought it was a good case because it's spacious and has a side grill for ventilation? I'm not too bothered though.

How much would I need to pay for good quality speakers? I bought £30 hp ones from a supermarket and I would say they are satisfactory but nothing special.

I've monitored my RAM usage and I don't think I would ever go above using 5GB at once. That gives me at least 3GB free RAM at all times.

I think I can narrow my upgrade needs down to a new monitor, new video card and possibly a PSU.

I don't want a wide monitor just a good quality image that makes pics and videos look good.

The most intense game I play is "Ultimate Epic Battle Simulator" this game can involve very large numbers of battle units in the game at one time (you can choose how many). I would like a video card that can support very large numbers of units. Or would this be the CPU's job? Is the video card's job just to display the images?

I also play minecraft and would like a video card that would render quickly and let me see far into the distance.

oh and I like to use the foldinghome project that let's you use processing power to help with projects. Apparently I can't use my video card for this because it doesn't support double precision calculations.

As for speakers i picked up some Rokit 5s for 100$ USD with amp and everything. The sound is superb. The bass is amazing, absolutely no complaints. I have also heard good things about all the Rokit speakers! Just sharing my expirence and Im sure these guys can find u great speakers also.