We were there from February 17-23 this year.
Per touringplans.com, observed crowds in all 4 parks were 10/10 the entire President's Day Weekend (2/15-16) and for President's Day itself, and remained high (average of 9/10) for the rest of the week.
For the Princess Half Marathon the next weekend, crowd levels ranged from 8-10 out of 10. We didn't really see any noticeable difference in the crowds from one day to another or one park to another at any point during the week -- they were all crowded, every day. Note that anyone wanting to visit or leave the Magic Kingdom on Sunday, 2/23 (the day of the half marathon) via car or bus had to put up with a 1+-hour traffic delay which lasted from early morning through lunchtime, and reduced the roads around the Magic Kingdom to total gridlock.
In short, regardless of which end of the week you look at, I'd expect the parks to be extremely crowded, and Disney will presumably, as it has for the last few years, NOT make any increase to park hours or add any extra magic hours to the holiday week to compensate.
My advice would be to just visit when it's most convenient for you, but adjust expectations ahead of time! My family still had a great time, but we had to rely more heavily on rope drops and EMH to get things done, and sacrifice a few of our usual must-dos, to compensate for the higher crowds, longer wait times, shorter park hours, and dearth of "day-of 4th FP+" availability.
If we had our druthers (we didn't, as our arrival/departure days were dictated by lower flight costs alone), we'd probably have arrived on Saturday or Sunday (during the President's Day weekend -- yes, it would have been crowded, but so was every other day that week), and left the following Saturday to avoid the transportation messes caused by the half marathon on Sunday.