Zoom lens advice needed
I have a 45-200. It is relatively big and heavy (and I'm trying to get rid of it as a result). I would never drag my 45-200 to a music festival let alone something bigger.
Also, an issue that is discussed here from time to time is people being denied admission to music festivals because "professional" cameras are not allowed. The people at the gate define "professional" as "big". You may not be able to get a 45-200 in there (or be seen using it inside, at least).
One of the 24-480mm equivalent ones? Only the 100-300 (200-600mm equivalent) will cover that same distance. The 45-200 (90-400mm equivalent) will be a little shorter.
In general, I recommend getting closer :). It improves everything. I've never brought anything longer than my Oly 45mm to a music event.