Business lunch ON THIRD in the 40's
If it has to be ON Third Ave., rather than within a half-block east or west, I suppose Dock's Seafood (NE corner, 3rd Ave/40th St.) would do. Certainly not the greatest, but it's within your geographic parameters and is also a "business lunch" kind of place. Also, Smith & Wollensky is right on Third Ave. (NE corner 3rd Ave/49th St.) - steaks & chops.
If you can go a little east or a little west of Third, and if price isn't an issue, Sushi Yasuda (204 E 43, between 3rd & 2nd) would probably be impressive.
Capital Grille (155 E 42nd, between 3rd & Lex), or Sparks (210 E. 46th, between 3rd & 2nd) - both steakhouses.
Avra (141 E 48th, between 3rd & Lex) for pretty good and a little upscale Greek - seafood emphasis.