Lensbaby Macro Lens Kit + Oly 45/1.8
I just had the opportunity to try this combo out, albeit under conditions which preclude precise accuracy. Lensbaby sells a a set of a +4 and +10 closeup filters in 37mm thread, so they mount directly onto the Oly 45/1.8 lens.
From what I could determine, the +4 lens gives a magnification ratio of about 1:3 and the +10 lens gives about 1:1.75. When I can borrow an appropriate tripod setup I will recheck this more precisely and upload photos. In this attempt the IQ was quite good with the +4, but less so with the +10, but this could have been the setup and my technique.