How good are 4/3 lenses on m4/3?

It seems that 4/3 is a dying mount and so there are a lot of quality 4/3 lenses on the used market. Not so with the premium m4/3 lenses as the demand is much higher.

Recognizing that I'd be giving up some of the size/weight advantage of native m4/3 lenses, I've been contempating getting a 4/3 to m4/3 adapter and buying some 4/3 lenses as a way of expanding the range of lenses I own. I shoot with an E-M5 body and would probably get the grip if I end up with bigger lenses.

I'm wondering if anyone has any experience to share here. Most specifically, I'm wondering about AF speed and accuracy.

Thanks,

Rey
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