Well on easywdw when Josh puts a number of 5 or 7, he means all the parks as a whole, not just MK. So even if the parks as a whole have a rating of 7, that doesn't necessarily mean that the MK wouldn't be a great park to visit that day.
It all depends on if the MK is hosting the Halloween party or not. Which it probably will be on a Friday so I say go on a Friday.
FWIW, we went in Oct of 2012 and followed Josh's recommended parks every day. Yes, that mean we went to the MK on days it closed early for the party. However, we had very good luck with lines. I would say our average wait was 10 minutes and the longest we waited was 35 minutes for Dumbo.
Now things will probably be different due to FP+, but I would still go to the MK on a friday. Get there at Rope drop and follow Josh's cheat sheets if they work for you.