No stuttering but started a race at Cascavel at 6 AM which led to general poor performance even with Shadows on medium. Changing to 10 AM FPS back to normal.
I have them only online ... at evening and night as for most of us busy in the day.
Strange but I think they began just after the update with the Boxers !
EDIT: I'll test something on monday:
starting a server from our remote server without matchmaker and only using the IP adress ... just in order to test if those problems don't take their cause ... from Steam for example.
If out of the server list it still happens ... it'll be already a possible cause out of the way.