Agreed, the F3HP excels with great eye relief and good contrast. The all microprism screens are awesome when matched with appropriate lenses. The Pentax LX's FA-1W is very close to the F3HP for use with eyeglasses, but has a larger image which is definitely contrastier. The LX's contrast is what really sets it apart, IMO. An LX screen in an MX is a great combo in a fully manual camera. Few viewfinders are as good as the OM-1's, except its brightness seems to come at the expense of some contrast, which makes it a little harder to find perfect focus on its field. Its magnification helps with using focusing aids, though. The MX has similar magnification. Screens for OM series cameras are still easy to find, as are most F3 screens. Common LX screens are still easy to find. The best viewfinder I've found in an M42 camera is in the Fujica ST 701, 801 & 901-big, bright, great contrast. Not great with glasses, though.
Maybe an AF camera with focus confirmation for MF lenses would be a solution. I just picked up an N8008s and found the stock screen much better than I expected for manual focusing anywhere on it. I like a plain screen so I would not expect it to be adequate for you, but as with most other AF cameras it has the in-focus indicator, which could be a lot better for manual focusing than focus aids if you're having a problem with even split image aids.