If memory serves, Whatman 42 is intended for vacuum filtration. Assuming that's correct, it would be a miserable choice for gravity filtration.
Chris is correct---I used Whatman #2 for filtering my solutions that were headed for precipitation. It is fast and retentive, although there were occasions where I'd have to re-filter the solution until it was clear. That's the price you pay for having a fast filter. Otherwise, they are subject to premature blockage. Whatman #5, for instance, would be a poor choice for filtering first run materials. I used that grade exclusively for filtering my re-refined gold. Because the solution was virtually free of contaminants, filtration was reasonably fast.
I, too, liked the old Sharkskin filters, and used them exclusively for filtering polishing wastes. I wasn't concerned with traces of contamination following the solution---it got removed in the final filtration. Sharkskin was one of the handiest of all filter papers---just a little too open for fine filtration. Again, that's the price you pay for speed.
Harold
edit: a search reveals that Whatman #42 is satisfactory for gravity filtration, but is very retentive, thus slow.