I already have a 144hz monitor

And when my 200fps drops to 150 I can see & feel it. ( its still above 60-80 as u say )
In theory you are right, but nothing is less true. Ask any real gamer if he/she can feel/see the difference between 60 and 100 or 100 and 200fps.
Another reason for my upgrade are ofc the new upcoming games such as far cry 4 etc.