This thread certainly has been an interesting read!
Just a quick note on people experiencing varying performance on similar hardware: CPU and GPU are not the only factors at play here. Your memory speed (not size) also tends to impact games heavily. Games love fast, low latency RAM, even to the point where the same RAM speed can show different performance levels based on their timings. People sometimes tend to think that buying fast RAM and plugging it in will have it run at whatever speed it shows on the box, without instead entering the BIOS and simply changing the RAM to it's XMP profile and the voltage it says on the packaging. For those who avoid overclocking, this could be a step to look into, as if you're not overclocking and not monitoring your memory speeds, you could well have never entered your motherboard's BIOS tuning section ever.
I've sometimes seen upwards of 20% increases in frames due to this so it's well worth looking into or at least checking anyway!
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Anyway, in my case with the venerable old i5-2500K @ 4.4 GHz I'm running into some iffy frametimes in AI races causing visual judder despite the game reporting a close to steady 60 fps, which I'm 99.9% sure is down to a CPU bottleneck. I tend to opt for a vsync'd 60fps as the minimal input lag introduced when using it in combination with a one frame render ahead limit annoys me much less than stutter and especially tearing, which only really disappears in racing games and sims at 120 fps and above, not something I can hit all that often at 1440p with a GTX 1070 in the very few GPU limited games I now have without bringing down settings.
In most gaming cases I'm CPU limited, and with temps still holding very steady after a thermal paste change about 3 months ago there's not a whole heap I can do to get a smooth running full grid AI race. I'm content if games can hold above 60fps as a minimum, but drop below that and I start getting annoyed.
Unless there are some huge optimisations in the physics part of the engine (the bit that is causing this for sure, other UE4 games for the most part give me no problems), it could be ACC that finally pushes me into an upgrade. AC did get a big AI physics optimisation update just before that hit 1.0 and had steady improvements throughout it's early major updates, but I suppose after nearly seven great years with this chip I guess I needed something to finally get me to consider moving on. While I've certainly had some less than ideal experiences with other modern games (Battlefield 1 was a nightmare!), considering I've put over 1200 hours and counting into AC it's probably natural I'd want a better experience with the sequel!
I've considered the cheaper side-grade option to a i7-3770K, the absolute best my current motherboard can support, as the hyperthreading there would no doubt help the situation, but with my motherboard showing some signs of age it's probably best I put this rig into retirement, taking only the 1070 with me.
I'm very seriously considering jumping ship to AMD as Ryzen has impressed me with its reported price to performance ratio, and despite still trailing Intel in single-threaded performance by a little, I'm experiencing more and more games making use of more than four threads which will probably only increase as time moves forward, and in general use strong multi-threading is finally starting to break out a gap over strong single-threading, especially when multitasking or doing anything related to video.
I'm thinking I'll probably go with a 2600x for now. The temptation is there to go all in and get a 2700x for the extra cores and threads, but with prices for good DDR4 sticks still ridiculous and showing no signs of dropping in the near future, I need to cut my spend somewhere, and having learned lessons from cheaping out on motherboards and PSUs in the past, I'm not gonna cut any corners there. My OC'd i5 could well have better single core performance compared to any Ryzen chip right now, but I don't foresee this being a huge problem for any racing titles at least unless I want to fire up older gMotor sims for a quick spin, and even then I should still stay above 60 fps. R3E and RF2 are the only modern sims I could see having issues, but even then I think with my rather low limit I should be OK, and in RF2's case that is sure due for a whole heap of optimisation on DX11 anyway.
With the AM4 socket also sticking around for another two years at least compared with Intel's current socket, which is probably on its last legs, I've also got plenty of future options to work with and could very easily to upgrade to 8 or possibly even a theoretical 12 core, which I believe could well be necessary if I'm to also jump into VR in the future which basically requires a beefy CPU alongside a good GPU to run at 90 frames in CPU heavy situations.
Whenever I get this done I'll update the thread with my findings as it seems the jury is still out on Ryzen being worthwhile for games compared to Intel. So long as I can hit a smooth unwavering 60 with vsync though, I'll be a happy chappy. Anything better is a bonus!