A thank you to B&H Photo — after the oddly disappointing performance of the 1st evaluation sample of the Olympus 60/2.8 ED macro, I now have a 2nd sample, which appears to be superior to the first sample (assessment/comparison coming).
B&H Photo has the 60mm f/2.8 ED macro in stock as this was written.
In shooting the two samples of the Olympus 60/2.8 ED, I came across a bit of surprise: significant field curvature at ~1:25 reproduction ratio.
Field curvature is not something I expect to see in a telephoto macro lens, at least not a 60mm focal length. And it helps explain the somewhat puzzling results with the first sample; field curvature in combination with a lens assembly error can be very confusing to evaluate.
For more on field curvature, see Making Sharp Images.