[Guilla]

As other already stated here, from my part, I have found a PLAN B SOLUTION :

PT is playback smoothly, without any spikes at all, when ALL THE PROTOOLS WINDOWS are reduced. I've looked at the CPU usage and the spikes are gone.
I can EQ like that with the EQ window really easily.

So it doesn't seem to be related to any third party plugins to me. It seems to be a graphical problems !!!

Perhaps if we reduce a bit the amount of informations in PT edit windows (since the mix windows is slightly less buggy) it'll help ?

Anyway, I'm pretty happy to discovered this, since it's the first time that I've found something that looks like a potential solution for printing my tracks without any hassle.