It seems that in general those horses carrying the least weight (ignoring apprentice claims) pay more than the top weights. And also the horses that draw the wider barriers pay more than those with the inside barriers. IMO, weights and barrier draws are overrated, but that they still influence many punters bets, so hopefully that translates into some potential value bets.

Could someone with a database run a test for me for both the win and the place?

Saturday Metro tracks only.
Good and Dead tracks only.
Ignore 2yo, maidens and jump races.
Only consider those horses carrying the least weight in each race (ignore apprentice claims).
Of the remaining horses, only consider the one with the widest barrier.

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...time held me green and dying, though I sang in my chains like the sea. - Dylan Thomas