Economist in the civil service here. I wouldn't sweat this decision, unless there's a transparently better alternative. It sounds like good progression for you, from which you can look for an even higher impact role.
My main reaction (rather banal): I think we shouldn't use an acronym like IBC! If this is something we think people should think about early in their time as an effective altruist, let's stick to more obvious phrases like "how to prioritise causes".
One issue to consider is whether catastrophic risk is a sufficiently popular issue for an agency to use it to sustain itself. Independent organisations can be vulnerable to cuts. This probably varies a lot by country.
This book is a core text on this subject, which explicitly considers when specific agencies are effective and motivated to pursue particular goals:
I'm also reminded of Nate Silver's interviews with the US hurricane forecasting agency in The Signal and the Noise.