Thanks so much for taking the time to write that post mate. I really do appreciate it, I got this game to join my Dad who's a retired Vietnam vet who's just gotten into gaming and I wanted to be his wingman but we can't get it to work on his system or mine. We've only tried single player so far, and we're kinda stuck here. When it didn't work well on his system, which is very entry-level, I tried it on mine and was very surprised to find the exact same behaviour.
I usually play FPS games and my system is tuned pretty well, I'm a bit of a tryhard. I use an OC'd 1070 driving a 1440p GSync monitor at 165Hz, RTSS and Afterburner with a custom OSD which monitors frametimes (among other important stats), bitsum parkcontrol to set the 'highest performance' power plan (on always) for my OC'd 5820K@4Ghz (it can go higher but it does 4Ghz at stock voltages and that's plenty on this CPU), 16GB of overclocked RAM (3400C14) with tweaked timings for maximum bandwidth.....Being an X series motherboard the HPET is enabled and works well. Latencymon is installed already and latencies are always low on my system and other games don't suffer from any input lag issues at all.
I'm quite comfortable with altering settings to achieve higher framerates (especially higher minimum frametimes to avoid stuttering)/lower latency/GPU limited behaviour/etc and always have success with other games but no change to the settings seems to make any difference here.
You've given some really good advice and I do appreciate it but it seems to be something specific to IL2 which is messing with me here. Even on Dad's slower PC, there's no input lag noticable between keyboard inputs or joystick triggers and windows itself, but the game just doesn't respond in the same manner as the rest of the system