Yet another sensitivity problem, sorry :)

Yesterday, I launched quakelive as usual, and my sensitivity was totally wrong.
It was very high compared to what I usually play with, and felt like there was some accel.
Of course I didn't change anything.

My original settings were :
Steelseries Kana
No drivers
Windows sens 6/11
Quake sens 2.1
in_mouse 2
cl_mouseaccel 0
MarkC fix

This gives me an approximate 15cm/360

I tried to :
- Copy/paste my backup cfg files in QL directories
- Reinstall QL
- Try with QLPrism
- Remove and re-apply MarkC fix
- Restore a windows recovery point

None of the above worked.
So, as I couldn't find any solution, I tried to lower my QL sens
to find my sens again. I found out a value quite close, but that wasn't as smooth as it used to be.

But I noticed something very strange, if I tried to put back my original QL sens, and put something like cl_mouseaccel -0.8, then the resulting sens was pretty close to what I used to play with.
So I was like, wow, do I play with negative acceleration ? Do I really need it ? Oo

As none of the settings suited me, I tried something different.
I installed the mouse drivers.
Driver sets default DPI to 800.

In QL, with 2.1, it was quite fast.
So I decided to use m_cpi parameters and set it to 800.
Of course the sensitivity went really slow, so I had to set it up to 12 or something like that, but I didn't really like the feeling of it.

I went back in the driver, and set DPI to 1600.
Back in QL I put m_cpi to 1600, and had ofc to increase the sens.
I put it up to 24 (!!!), and ended up with a sensitivity that suits me, even better than the original one (rofl).

But 24 is a really high value, I'm quite surprised.
Do you, or any player you know use such value ?
Is 1600 DPI too much ? Is quake able to be precise with sens @ 24 ? Should I lower m_cpi even if the mouse runs @ 1600 ?

Sorry for the long post.
This sensitivity thing is driving me mad. It happened a few times, but usually I just have to relaunch quakelive and it's back to normal.

I have been struggling quite a lot and would really appreciate any ideas :]