Not sure what makes you think Gawn has a bigger ceiling.
2015 stats:
Martin : 20 games, 7 scores over 120 (35% of games), 11 games over 100 (55%), 2 scores of 76 or under from 20 games (10%).
Gawn: 13 games, 3 games over 120 (23%) 4 games over 100 (30%), 4 scores of 75 or under from 13 games...