Possible Clues:

• Go beyond the prescribed limit
• Do better than former top player on radio
• Get more from such seed, by the sound of it
• Do more than is warranted by
• Go beyond - top
• Former class player said to go too far
• Outclass old tennis ace utterly
• Go over the sound of what was formerly sown, perhaps
• The way to get more from what's sown, by the sound of it (6)
• The way to get more from what you sow, by the sound of it