I'm a fan of Google Flights and used it to track my Seattle-->Heathrow-->Dublin and Heathrow-->Seattle multi-city flight itinerary before buying. I didn’t start looking as early as you are, but there definitely were very wide price swings. I finally jumped at the bait after seeing the price go down again.
I saw no dramatic price differences that I could tie to purchase dates. I did see significant price differences tied to the day of the week I wanted to fly. Fortunately, my preferred Wednesday flight days both directions were the best. Lucky me.
If you use Google Flights over a period of time, the graph will show the rises and falls in prices and you can see what the most common price is. I'd bite if the price for your dates falls below that most common price.
However, keep in mind that the lowest price shown may not be for the kind of ticket you want to buy. When you click through to the airline, you'll be able to see the different kinds of tickets available, their prices and what those prices allow you to do.