When you are looking at your acceleration curve, it's nice to know roughly how fast you move your mouse when performing your fastest flick. Fortunately, there is an easy way with the interception driver.
Close InterGUI.exe and interaccel.exe so that all acceleration is turned off. Edit your "settings.txt" with notepad and go down to the very bottom where it says "FancyOutput=0" Change that 0 to a 1. Now run interaccel.exe (not the GUI), and a command window will pop up showing your settings and a live output of your effective mouse speed and sensitivity. Move your mouse around with some flicks and get an idea of the biggest numbers you're seeing. This is the point where you'll want to have your acceleration curve to already be at your sensitivity cap.
Now, be aware that the FancyOutput option introduces input lag, so you won't want to play games with it. This is why when you run InterGUI.exe, it immediately stomps on FancyOutput and forces it back to 0 when it starts the acceleration back up.
If you aren't using the interception driver, you can still use the following method to determine your mouse speed:
First, save your current mouse accel settings to a profile. We are going to ruin them, and you will want to have a backup. Next, get comfortable navigating the GUI with just your keyboard (using tab, shift-tab, the space bar, and enter), because I'm about to make your mouse difficult to use for the sake of science.
Good with that? K. Now set your post scale values to 0.001, acceleration to 10000, and then set your offset to 10. Either let the sensitivity cap raise itself or set it to 0. Save changes, and give it a test.
Your mouse should be impossibly slow to move until you hit the offset, at which point the accel carries your sensitivity way up. That should give you a feeling for how fast you need to move your mouse to hit 10 on the x-axis.
Now, using keyboard to navigate the GUI, raise the offset and try different values. As you go higher, you should find the point where you no longer can get your cursor to move. This should give you an idea of where on the graph you will reach. I find on 1000hz and 2300 DPI, I can still move the mouse with quick flicks reliably at an offset of 60. Now is a good time to restore the settings you saved to a profile.
Using this new information, you should always aim to have your acceleration curve hit your sensitivity cap before your maximum speed. It doesn't need to land at the cap right as you hit your max speed - my curve hits my cap around 30, but the fastest I move my hand is closer to 60.