I say you wait untill a mid-August weekday. Crowds should die down by then, and they should be the same as early June weekdays.
I buy the fastpass now. It works for me. Sometimes you just don't feel like waiting. Use it on V2, that line is horribly long, and it breaks down just about every hour, so be carefull when/if you use your fastpass on it. I used it two times on V2 and both times it broke down while I was in the station.
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There is no such thing as a stupid question, just stupid people.