I would agree with Val. That you feel torn can be reframed as having two equally good choices (just in different ways). Situations where there is really no "wrong" decision are excellent for learning decision-making skills.
And he has to live with the outcomes, so what he values for this coming year should hold some weight. It might also help to discuss what he actually values about each scenario, and then consider whether there are other solutions to meeting those needs (e.g., extracurricular math or sports), or what tradeoffs he would take in order to have certain kinds of opportunities (social or academic--or social and academic, if the students in the GT 7th grade class might be closer to intellectual peers).
