If I wanted to know that, I would install msi afterburner and I would activate the monitoring feature it comes with. I would enable FPS, RAM usage, CPU usage, GPU and VRAM consumption. that way it would be very easy to say which part of your computer is limiting your game(any game, IL2 included).
For example:
If you have all that turned on, you would open up your game and all that data would be displayed on the screen as if it were Fraps.
With the game running and the data on the screen:
if the RAM consumption is next to 100% of your actual physical RAM(8GB in your case), it would be safe to say you need more RAM. Your computer in this case is using virtual memory for sure, so it is using the hard drive as RAM, you can get more FPSs if you have more physical RAM since it won't waste CPU cycles to fetch data from and to the Hard drive.
If your CPU is at 100% and your RAM is below lets say 75%, then your CPU is limiting the FPSs.
If you suffer from stutterings, check your RAM consumption, if its near 100% and you have stuttering, you need more RAM.
That said, 75 FPS is a very good number if it is stable and it does not deviate from that constantly.
I don't know how many FPS you should be having if you had the best/optimal rig, sadly. I have less than an hour of gameplay time