I used to keep my rift volume at around 10-30% depending on content, 30% usually being uncomfortably loud. Now I find myself regularly bumping it to 100% wishing it would go higher, I could easily see myself needing 150-200%. I believe this happened after one of the 1.19 beta updates a week or two ago. I can't think of any other reason why something like that would change besides an undocumented beta update.
For the time being I've unscrewed my rift headphones and started using my usual wired headphones since the volume goes as loud as I need it.