One consideration with your current question - might it be more impactful to move people from a 5 to a 9 on that question, by informing them about the principles of EA, rather than taking someone who's already a 9 to start with? Of course there's still value in pointing the 9 towards good resources, but you might expect them to find those themselves if they already care so much.

I like your question of "On a scale from 1-10, how much does maximizing positive impact guide your career thinking/planning?"

However, 10 = "It's the sole deciding factor" is phrased in a way that's worryingly demanding. I think many EAs wouldn't see maximizing positive impact as the sole deciding factor in their career thinking/planning. Where the job is located and how much it pays could easily be other deciding factors.

Given this, I think some people who might become hardcore EAs would be wary of rating that question highly - they might just give a 5/10. 

So maybe you could phrase 10 differently, like "It's my main priority" or "It's one of my top factors", which are both slightly softer than "It's the sole deciding factor".