Good luck Mr. Surapon. I hope you enjoy the MK II. I've got GAS too but am getting help by selling alot of lenses I honestly just don't use. This forum is good therapy
. I've sold my older 1DIV and 6D bodies and will keep my 1DX, 5D3 and 7D2. I've had the 100-400 twice and will sell the one I've got now as I typically shoot with a 70-200 2.8L II with a TC2.0X with gives about the same range but much sharper and easier to use. The 400mm f5.6L is also extremely lightweight and super sharp, oh, and cheap!
Selling some of this gear will also prevent me from lugging 6, 7 or more lenses at a time on an excursion. I tend to carry way too much and quickly regret the added weight.
In an effort to travel lighter, I started shooting mirrorless with Fuji but again, I find myself collecting lenses and the bag is getting filled up again. Fuji is great for travel and quick shots but it will never replace my Canon gear.
Best of luck Mr. Surapon. We'd love to see some shots with the MK II when you get it.