I found something interesting.
After several tests, the non-local video memory usage, starts to grow, till 250MB.
I also see in task manager that my system is using 500MB of ram, while it uses usually 200-250MB.
There isn't any process using those extra 250MB, so, it must be memory used by the kernel or a driver.
When this happens, my framerate grows a 10% in all the games.
Why ? I dunno yet.