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proteus -- You can take Suit Supply off your list. They do outlet sales twice a year (at the most) and that's it. Everyone else should have at least one good sale between now and Christmas.
Often times the very best price is towards the end of the season, but you have to be willing to risk a stock out. This depends on the retailer, but it's worked and not worked for me with J. Crew.
Look through old posts on dappered.com from last year. There's no guarantee that things will shape up the same way, but it gives you a rough idea.
I tried to get a price adjustment from Bonobos after the last day when they are allowed, which is different from the last day I could return the item. They would not give me a price adjustment, but would allow a return. So, be sure to read the fine print if you want to play that game.