On the GX7, I can hand hold down to about 1/10s at about 60mm, whereas on the OMD, I recall being able to hold down to about 1/5 so the 5-axis is better for shorter focal lengths than the GX7. However on the 100-300, I find the Panny OIS in the lens a little better than the OMD's 5-axis at 300mm. Also with OIS, it's on all the time, so it's easier to compose, while with the OMD, you have to half press the shutter.
Nontheless, with the Oly 60mm macro lens, the GX7's IBIS is still very useful. The following shot is similar to the earlier fly shot, but uncropped and without flash so it only has GX7 IBIS an no advantage from the flash. You can see that it is still very sharp even handheld with the GX7 IBIS.