What would you value and how would you proceed in this hypothetical employment scenario?

Suppose you work in a job that pays well, is moderately challenging and that you are comfortable in. However, it is often somewhat boring and doesn’t seem to have much room for advancement.

You are offered a position with another organization that is one of the top players in their domain. They offer a chance to work on very interesting projects with major companies as well as working with some very skilled people in your line of work that you could potentially learn from.

The catch is that you must take a 30% cut in salary from your current position and begin near the bottom (at a just-above-junior level) with a role that might be difficult or not exactly suited to your abilities. This organization does, however, promise to expedite your advancement if all goes well because they recognize your abilities and experience.

I know this is complicated but I’m curious how some of you would approach making a decision about something like this. If its more helpful, assume this is a software related industry we’re talking about.