Ouff.. Yeah ok, you need an upgrade!
I looked at some older benchmarks to get some perspective on the performance.. about 30-50% performance of a gtx 260, which is about 30% of the 1050 ti.
So definitely your bottleneck here!
25 fps should be easily doable with a non-k i7 2600! How many overlay HUD apps are you running? Sadly these AC overlay "apps" are all lowering the CPU headroom.
The difference for me, no apps vs my normal racing HUD is about 40%.
But anyway, you should have around 50 fps even with a lot of apps.
That's in theory okay! Windows 7 and the newer ones are very good at putting everything that doesn't have priority into the page file on your hard drive. As long as you're not hitting the 8 GB, it's okay in my experience!
But additional 8 GB won't hurt either way so go for it
Now this is a bit more complicated.
When you read out the application threads of AC via process explorer (little exe you can download for free), you'll see that AC only uses 2 big CPU threads and a few little threads.
This means that in simple theory, AC can only use 3 CPU cores. 2 for the big threads and one core doing all the rest.
So in theory, you'll only see:
100% divided by your 8 CPU threads (4 cores + hyperthreading) = 12.5% per CPU thread maximum load.
12.5% * 3 = 37,5% maximum load caused by AC.
However your CPU can still be the limiting factor, because you can't split the AC threads further and the other CPU threads simply sit around, doing nothing...
Now Windows does some magic shuffling, which you can imagine like this:
Slowing everything down to a single CPU cycle:
Core 1: calculating thread 1 of AC
Core 2: calculating thread 2 of AC
Core 3: managing everything else
Core 4: caching for what comes next
Virtual cores (HT): caching for what comes next
Then the next CPU cycle:
Core 1: caching for what comes next
Core 2: caching for what comes next
Core 3: calculating thread 1 of AC
Core 4: calculating thread 2 of AC
Virtual cores (HT): managing everything else
Now this happens with up to 3.8 GHz for your CPU. Taskmanager etc having a tick rate of 1 second, you're seeing at 3.800.000.000 CPU cycles AVERAGED!
What I want to say:
Assetto Corsa can't use all of your CPU. So you can still be CPU limited with an overall CPU load of only 12.5%, which would mean a single thread application using that one core to the maximum.
However due to the averaging from TaskManager, you'll see ALL CPU cores used to some extend and get the impression of the CPU having some massive headroom.
But it has none.
Easy solution:
The graphics card load works differently. All applications can use it to at least around 94% (sometimes some applications have issues using everything but it's always at least a bit more than 90%!).
So if your graphics card is NOT at 90%+, your CPU is the limit (or a FPS limiter, vsync or something else that restricts the FPS).
However:
The render stats AC overlay app can show the MAIN_T and PHY_LATE, which both can indicate a CPU limitation and are very useful.
Hope that helps! But I completely agree that you need a better graphics card and that your CPU is a LOT better than your current 5670.