Hm, this seems tricky for an intro pitch, if we're talking about careers in areas this community considers especially high-impact:

• In global development, non-earning-to-give careers in the community seem to be rare and pretty different from one another, so estimating the (near-term) impact of a typical such career seems tough.
• In existential risk reduction, it seems like quantifying the value of anything quickly gets into huge numbers, lots of guesswork, and weird questions, while in factory farming, quantifying impacts quickly gets into tricky inter-species comparisons and focusing on non-human animals. For an intro pitch, my intuition would be to lead with better-grounded and more intuitive content.

On another note: on the off chance you haven't seen them, you might find the short introductory presentations here useful.