Albert,
I own the old manual-focus Zuiko 350/2.8. According to published reports, NASA tested then selected the Zuiko 250/2 for earth-observation photography during shuttle missions. Their tests determined it to be the sharpest telephoto lens they had ever tested at that time. It's only drawback is the weight. If you can find a well-preserved specimen for a good price, buy it. Optically, that lens is as good any manual-focus telephoto ever made. I use my old Zuiko 350 regularly on my E-510 and it outperforms all of my newer Zuiko E-System zoom lenses. I do not own nor have I ever compared it to the image quality produced by the ED 150 or ED 300 lenses. I'm sure those new auto-focus lenses with digital-specific design would win a shootout but their prices are way beyond my reach these days. So I'm happy to manually focus with my 350. I find that I pay more attention to composition with manual focus lenses and I typically end up with a higher percentage of keepers.
Mark