Anyone use the Oly 50-200 f/2.8-3.5 on OM-D (or other m4/3)?

Hi, I just bought an OM-D and am still exploring which lens to buy.

One interesting lens is the Olympus 50-200mm f/2.8-3.5.  It is a 4/3 lens (not m4/3) so I understand it needs an adaptor.  There are very good reviews on the image quality and the range/aperture/price are all very attractive.  Although the adaptor still gives AF ability, I am concerned about the AF speed.

Does anyone have experience have this lens?  And how's the AF speed with an adaptor (not just with this lens but with other 4/3 lens in general)?