First world problems

[Drona]

Also you need to buy and register both expansions if you want to level beyond 50 (Heavensward and Stormblood, but the later comes with the former anyway), as your exp will cap out at 50 otherwise - buying the expansions is the only way to level beyond 50.

So they're definitely worth investing in for that alone.

I think I am getting expansion but I think I phrased the question incorrectly.

I want to make the best use of 100% exp buff and I don't know when that will get turned off so what is the hardest to level range? 1 - 50 or 50 - 60?

If 1 - 50 is the hardest then it make sens to level the WAR to 1- 50 now while the buff is active.