I can't seem to fix it. I just want it fixed, I'm tired of having to "adapt" to this input lag when something is wrong somewhere and I can't find it.

Here are all the latency I've measured/calculated.

Tablet polling rate is 230hz = 4ms frame interval
Unlimited fps DirectX and 1 pre-rendered frame: 2ms frame intervals + 7ms extra frame.
Monitor display latency: 1ms
Monitor refresh rate: 144hz = 7ms interval
Average measured interrupt to process latency: 2 µs
Highest cpu latency measured: 155 µs

Nothing is wrong with any of my hardware and it's all top of the line equipment. All my drivers and bios are up to date. Memory check showed no bad results. I have 32 to 50 processes running on average (depends what I'm using), everything unnecessary is closed and all extra services are stopped. I've tried fresh clean gpu drivers, and tweaked. I've tried default audio drivers and currently I'm using ASIO sound drivers. There are no problems with the audio, it's really in sync in fact. I've tried using various programs and tweaks as you've seen my previous threads, none work as intended and some are just placebos. Also all mouse acceleration is disabled everywhere.

So where is this problem coming from? My conclusion are:
there is something wrong with the input thread for osu! (being starved when the rendering thread is blasting out 5,000fps, lower fps seem to track the cursor better but frame intervals become unbearable. I just did research and if I'm wrong then this isn't it.)
Something possibly went wrong with the implementation of raw input (Which I use and I feel there's a sort of mouse acceleration effect going on).
Something is possibly wrong with the rendering pipeline for osu! (possibly too much pre-rendering which it has claimed to not be the problem)

It could also possibly be the g-sync module I installed in my monitor. I've got it disabled when I play osu! but it can only manage the scaling by using the gpu, which I've heard that it causes lag if you use gpu scaling instead of monitor scaling. I'm not about to buy another $300 monitor just to test this though, nor am I going to buy another AMD card and waste this GTX 780 I have.

Outside of osu! and in other games I can't really notice the problem or replicate it the same way, seeing as how most games are a lot slower than osu! and don't demand such high input response times. Some games even follow cursor input a lot more precisely than osu! (Most fps games even with really high settings)

How did you manage to use ASIO with osu! ?

Have you tried using other completely different PCs to see how is the problem in those computers compared to your PC?

I just uninstalled my sound drivers (Realtek hd audio, a lot of problems with it, most of my DPC was coming from it) and installed the ASIO ones, from there it's automatic. As far as I can tell the audio is a lot better and precise. Much better than before, but the cursor latency is a problem that still stands.

I've gone through a variety of pc parts and I've tried my laptop. Others are claiming not to have this problem so I really don't know what it is. I've used the following parts:

700 watt psu, 750 watt psu
i5-2500k, i7-4770k
GTX 570, AMD 7770, AMD 7990, and GTX 780
16GB RAM-1333, 8GB RAM-1600
Asrock Z68 E3G3, MSI Z87-g45, MSI z87I

only thing I've not tried is an AMD motherboard. With the cpu I've tried stock clock speeds, overclocking to high amounts, and I settle for a moderate overclock. I have all power saving states disabled and everything set to performance and fixed rates. With the RAM I just use the XMP settings and I haven't bothered messing with the clock speeds. Temps are fine, 30C idle, 34C to 38C under load across the board on all the parts.

As Full Tablet suggested, try a completely different PC, preferably that of a friend who claims not to experience any input lag. There is always a tiny bit of fishing-line effect, maybe you are just oversensitive.

FPS games are not that critical when it comes to "fishing-line" lag unfortunately, so it's not a great test. CS:GO has post-processing and pre-rendering up to 5 frames ahead which can't be disabled, and few people complain about it (everyone has to deal with it). When testing my reflexes in a CS:GO test map, I can barely make 1/10 hits under the 210ms mark, while I've tested as low as 167ms average in a browser test (human benchmark). The test could be inaccurate (map functions), but that is still a 43ms margin at least. I play on lowest graphics settings.

My only recommendation as a final test would be to try a B75 motherboard, or find someone with one and a similar setup. It's not a high-end board, and certainly won't suit your needs (I guess, no overclocking), but it's fairly cheap. Otherwise I'd have to concede that there may be something wrong with super-high FPS values, but I have never tested that myself.

I have a 144hz, no problems.

I've technically tried several pc by swapping parts out, I've built 3 different ones. Also I've used my laptop as I said. The problem persists.

Edit:
A co-worker of mine is going to get the same monitor I have but without the g-sync kit and I will try his monitor out to see if there are any issues. I still have the old board so if it IS in fact the problem then I can swap it out again. I would like to avoid having to buy anymore things just reconcile this problem.

Tried the other monitor, same thing.

I've illustrated how it feels when I play. There is no way this is a 1 or 2 frame buffer, something is wrong here.

Bump, still not fixed. I've tried doing a clean install of windows (currently using windows 7 64-bit embedded, thin client setup).

could be a problem with the game. peppy would need to respond in that case.

It isn't.

Try running windowed with unlimited fps and osu! focused, then run your mouse just outside the osu! window up and down with quick turns. Use a high FPS camera (iphone 5 will do if you don't have anything faster) to record the difference between windows and osu!. You should see 1 frame difference in responses in this case, which is what can be expected from any game running under desktop composed windows.

(note that you should be running fullscreen normally. if you aren't then lol)

During the menu it's fine though. The problem is when I go to play. I can feel it gets worse when playing certain maps too. Sometimes it gets worse from retrying. The lag sometimes builds up and eventually the game crashes. Currently I can't show you because I can't view the windows cursor while playing.

I don't see how it can change from the menu to gameplay.