4/3 Lenses on M43
I must be overlooking something when I think that 43 lenses should work no worse on an M43 body like the OM-D than they worked on a 43 body.
I.e they may not work as fast on the OM-D as the newer lenses optimized for the OM-D such as the 12-50mm, but I see no reason they should focus worse than they did on a 43 body like a 510 or a 620.
They work no worse than the lenses don on a Four Thirds body in live view mode . The E-P1, for example, is basically an E620 stuck in live view mode all the time.
If you have an E620, you know that this is... suboptimal.
There are a handful of Oly 4/3 lenses that were "optimized for live view" at the time of release. These include probably most usefully the 14-54mm f/2.8-3.5 mk ii and the Oly 70-300mm in addition to a couple of others. These lenses do "OK" on current M4/3 bodies, but they're still not as fast as PDAF on a DSLR.
Everything not CDAF enabled - especially SWD lenses - will be woefully slow.