I think the max ranking for Gasquet is top 15,
he is very talented, good tennis but nowadays the most important weapons for a player are the physical and the fighting spirit, you don't need to produce a high sophisticated/technical tennis, a basic style tennis ( good serve and solid defense on the baseline )+ good physical and mental/warrior style are enough to be in the top 10,
Gasquet doesn't have a solid physical, he is often injured, he seems to choke during key points and he has difficulties to win against top 5 players ( the psychological barrier is too high for him ),
that's why I think Gasquet can not be in the top 10, he can win one or two big tournaments ( ATP500, maybe a masters 1000 if he is lucky with the draw ) but win a grand slam seem to me an utopian view,
he is a good top 20 player and I think Gasquet will be happy to stay top 20
It's always been the case, you can't win by just having a superior talent no matter what era. In the late 1970s Brazil manager Claudio Coutinho made a famous quote about then 22 year old French midfielder Michel Platini (now UEFA President). Coutinho said about Platini "skill without effort is a total waste of time".
Platini went on to realise his potential, especially after captaining France to the 1982 World Cup semifinal and joining Juventus, where he scored lots of goals and won many honours both on and off the pitch. But Platini said that only when he joined winners at Juventus then he realised how hard you need to work to win. So when you get a player of Platini's skill realising his potential, then you get history in the making.
Gasquet has gone the way of too many French players of the last 30 years (LeConte, Pioline, Tsonga, Mathieu etc etc). These guys have incredibe talent and yet can't make a name for themselves, they just don't seem to have the will to win. Luckily for France, Amelie Mauresmo bucked the trend as she was going the same way until she won those two slams plus the year end championships between 2005 and 2006.