According to this, the 750 by some margin. I'm not sure what memory configurations they tested - and never forget that, while this is a good test, some cards do better with some games than others, regardless of how they compare in an 'average' head to head. That said, the 750 Ti seems to beat the 745 by some margin. The 745 you note has more memory - but DDR5 memory is much faster. DDR3 is last generation.
iMac Pro review