That your BenQ XL2420T has nothing to do with antialiasing. The stutter is caused by graphic card which is responsible for MSAA etc.
all graphic drivers updated etc ?
Is there a continous FPS drop or is it at like 200 then 0 then 200 then 0 etc...
I am 99% sure the monitor is not to blame, but test with anoher monitor too be sure.
Is AA very important to you??
disable AA in graphic drivers and enable it ingame, or the other way around...
Do what #7 said. If that doesn't work, reinstall your nvidia drivers.