I'm looking into gh5 as well. I was eyeing up the olympus 12-40 pro 2.8 and the 40-150 2.8 as an alternative native lens combo. They don't have ois but I wonder how well the ibis alone on the gh5 works with them. That glass might have a different (in some eyes better) character than the Panasonic's. Not sure though, I'm just asking.
Oops, just saw @Ivanhurba post. Thanks!