Not sure about Presidents Wknd, but MLK also has running races starting on Fri which will add people. The past couple of years, Fri and Sat morning haven't been too bad, but Sun has been really crowded.
We went Presidents weekend in 2013 and it wasn't that bad at either park. But when we went this year the parks were both PACKED. Every CM we spoke to mentioned how busy it was, and that they hadn't seen so many people during that weekend in a while.