MattUK here. Sorry for the lack of replies! I totally forgot this forum existed. Needless to say, I graduated from U of T several years ago. I did end up graduating with the Econ & Math Joint Specialist and also did the 1 year doctoral stream Masters in Econ (which I think has been merged into the regular stream now). I'm not sure my advice will be the most up to date anymore, but I'll check this thread periodically. For anyone considering graduate school, my advice might be more relevant. I'm doing a PhD in the UK at the moment, albeit in a different field (biomedical).
Thanks to the people who answered questions in my absence and for the rest of you I hope you found answers somewhere else!