It's always fascinating how a core update can act like a natural selection event for search results. I've seen similar patterns in competitive B2B SaaS niches - pages that were essentially invisible suddenly break through, while established content drops.
The 2.5 year page age is significant. That's long enough for Google to build some trust, but not so long that the content feels stale. The paid PR and backlink work you're describing sounds like you're building a proper foundation rather than chasing quick wins. I've found that in hyper-competitive spaces, it often takes several months for those signals to compound - and a core update can accelerate that compounding if the fundamentals are right.
Bing ranking ahead of Google is a solid sanity check. If you're outperforming DA 90 sites there, the content and link profile are likely strong. The fluctuation you're seeing now is probably Google testing relevance under new ranking signals. Worth keeping an eye on whether the page stabilises or drops back after the update settles.
Also, respect for sticking with it for three months - most people bail after two weeks when they don't see movement. That patience is rare.
