I started out playing at a very high sens (6cm/360), then lowered it a little, albeit still quite high, achieving some success (15cm/360) before continuing to lower it, until now I am at 50cm. It is in no way uncomfortable to me as it is an entirely different way of using the mouse - as high sensitivity players often use their wrist exclusively, I predominantly use my whole arm and use my wrist for fine adjustments. As the mousemat I use is 45x40cm, and I have a sizeable desk, I rarely encounter problems with mousing space.
I can understand why it feels appealing to play with a high sensitivity, especially after being used to it for so long - no doubt lowering it gives you better results in that you hit more, but it feels sluggish and restrictive, and you cannot turn around fast enough. Practicing for long enough would eventually relieve you of these problems while maintaining most of your improvements in aim, but it's not a given that you need a low sensitivity to aim well, rather, it's about comfort and preference.
In contrast to what a lot of people have said before me, strafe aiming is not ideal, and if it is used as the preferred or sole method of aiming, is flawed. The reasoning behind this is that many people, especially top players, can have very unconventional patterns of movement which are unpredictable and difficult to hit, so trying to steer your crosshair into these people with your movement is challenging to say the least, and could actually make you easier to hit, as you are moving less to avoid shots being fired at you and more to hit your own.
Even on such a low sensitivity as I use, I still don't aim exclusively with the mouse, and have trouble believing anyone would in this game - sometimes I put the crosshair near to the person and tweak it with movement (strafing/dodges), or put my crosshair in a certain place and wait for them to move over my crosshair before clicking. It's about being subtle and how much you can realistically get away with. However, the preferred method will always be to put the crosshair directly on the opponent with the mouse. If you can't do that consistently and comfortably, maybe you haven't found comfortable settings yet?
Please note that this doesn't mean you have to flick at uncontrollable speeds, rather, you aim as fast as you can comfortably hit. When you spot a target, get your crosshair as close as you can, and then tweak it for each individual shot. Prediction will always play a big part but is mostly learned from experience.
As for aiming well with a high sensitivity all I can suggest is practice and control. The ability to aim at any given pixel on your screen with both speed and precision is important regardless of whether you use 6cm or 60. Perhaps you could try lowering your FOV, however that's also a dangerous route to go down - mess with your settings too much, and you lose your sense of consistency.
To the person suggesting the G500 is better than the MX518 - insofar as you are using very high sensitivity, you may be correct, especially as you can disable prediction/angle-snapping, however for many people the MX518 is still superior as the G500 has been known to have positive acceleration issues.
