I was looking through a table of standard reduction potentials and the trend seemed like it correlated with electropositivity. Is it reasonable to qualitatively compare two metals to see which has a higher standard reduction potential based on electropositivity? If not, why is this unreasonable?
Your reasoning is reasonable. However, although we can make the association between electropositivity and reduction potential qualitatively, relying on the former one to imply about the reduction potential is not always safe. For instance, following the trend of electropositivity on the periodic table, we would imply based on the reasoning that you proposed, that Zn which has a greater electropositivity than Cu (check the table bellow) has also a greater reduction potential, which is not the case. When it comes to transition metals, there are actualy some other effects that play a role on the reduction potential of the atom, ex.: shielding effects, final electron configuration, etc. The bottom line is, although electropositivity could help to justify a certain trends in reduction potential, it should not be used to make rigorous predictions of these trends since it could easly lead to mistakes mainly when considering transition metals.
P.S. The table shows the trend according to electronegativity. You can visualize the electropositivity trend by inverting the color scale at the bottom.