Hello again, vahonen. Everyone has their own opinions about what are important features in a lens. However, there can be no doubt that a properly used A850 or A900 will mercilessly expose optical weaknesses.
I am not knowledgeable about Sony's current lens range or Minolta's older lenses, but based on nothing more than Photodo's old MTF charts, I think the Sony 50 mm f/2.8 macro is worth consideration as a general-purpose normal lens. It's very cheap and therefore probably mechanically poor, but it's supposedly the same optical design as the Minolta equivalent.
This lens has very impressive MTF curves at f/8, as measured by Photodo with the Minolta version. Even the very corners are sharp, and the 40 lp/mm values average about 70% across the majority of the frame. The tangential values also respond very well to stopping down, which suggests excellent control of lateral chromatic aberration. Of course you would need to research flare performance, bokeh, and other characteristics that are relevant to you.
Minolta also made a 50 mm f/3.5 macro: a five-element design from 1995. I suppose they didn't sell very many, but given its relatively recent design and unambitious nature, it's possible that this lens is a real stunner. But I don't know, of course.
Regarding the viewfinder coverage, the 98% almost certainly refers to horizontal and vertical coverage, rather than area. So if the figures can be trusted, the A850 has about 96% coverage by area, compared to the A900's 100%.