It was the best one the guy had. You get what you can. :P

Sounds like when my friend bought his "monster PC". Didn't ask me for advice but went to some local crap PC store, probably one of those who concentrate on business customers, and they didn't have anything else than mainstream and budget cards in stock lol. This is top of the line, the best you can get man.

That will be a substantial improvement. Your 750ti could have played Doom (2016 Release) just fine however, because I know someone with that exact card and an Ivy Bridge i3. However, they had 8GB DDR3-1866. Your issue was almost certainly two things :

1- Lack of Ram causing continual HDD fetching/access (this slows down a system like mad)

2- Default settings on PC games are notoriously aggressive on AA/etc. This is fine for mid-high to bleeding edge GPUs, but is disheartening to those with entry/value cards for sure.

Setting Doom to 1080/NO AA/etc (optimized to look good but not amazing, basically somewhere between gen 7 and gen 8 console settings) makes for a completely playable experience :

https://www.youtube.com/watch?v=ynhBzx9rqgU

Keep in mind Youtube has horrendous compression artifacts, so this would look much better in person.

Everything is 'outdated' depending on how one looks at it. Anyway, your new build should be fine. If you have a motherboard with the unlocked multiplier, then keep an eye out for a 4770K or 4790K, that would give you a CPU you could use for years and years to come (they can be overclocked to provide faster gaming performance than a new stock i7 5000 or 6000 series with ease).

And above all : update to Windows 10. You can still do so now for free despite the public 'this is ending in Summer '16' statements. This gives you access to DirectX 12, and will be supported far longer than W7/W8 in the future. Download 'classic shell', and install with all default settings, and you have a fantastic desktop OS. You should also disable shared updates, unhide hidden files/file extensions, remove the gigantic Cortana search bar on the taskbar, set taskbar items to 'combine when taskbar is full', and so on, basically un-dummying the default settings. I can help with this if you want.

And a BIG one, that you can do on your current system, is to open an elevated command prompt, and type the following command :

powercfg -h off

This will disable the hibernation file, which is an antiquated thing where it saves the entire computer session to a file on the hard drive exactly matching the RAM amount in your system. 16GB ram = 16GB wasted drive space. This is especially irritating on a system with an SSD. Of course if you deliberately use hibernation, then leave it on, but out of thousands upon thousands of people I've worked with in IT, I find that almost nobody does. Back in the bad old days, sleep mode was poorly supported and unstable (hardware and Windows both not being great at it), and so hibernation was more reliable way of saving your work on a laptop to come back to later without saving all of your open stuff and shutting down. Now, sleep mode is fine on modern hardware, going into a super low power state and coming back up reliably, making hibernation kind of obsolete unless you want to leave it in a frozen 'booted' state for an indefinite period of time.

Myself, I never use either, I save what I'm doing and shut the damned thing off. I have 128GB of Ram in one of my systems, that would be an unholy amount of wasted drive space lol.

That youtube link Arkaige posted was a good one.

Its a slower CPU than OP, with same GPU, and he plays around with Doom until he gets 60+ fps and game looking as good as it can on his system.

There are still area's where its so demanding on his cpu it drops down to 35-40 fps ranges, but its def. playable.

So OP, you need to buy a stick of 8gb memory and put in your system.
You need to use tuneing tools to give your gpu a slight OC, and then you need to play Doom 720p, and play around with the settings until your statisfied with the way it runs.

Just go from 4 to 8 GB on the RAM and pick up one of those cheap VR ready GPUs from AMD or Nvidia.  Doing a RAM and GPU upgrade like that shouldn't cost more than 350 or so.

RAM is definitely the bottleneck.

Just post your specs. It;s about time for me to upgrade.