"I also question effects of enhancing Math to his level to balance his day and not enhancing the rest. Wouldn't that make English and Science feel like not good subjects, despite potential for talent there too?"
My son is globally gifted. When he was 8 we were given the choice of grade skipping or subject acceleration. After much discussion he chose the latter. As a result he was accelerated 3 years in Maths and 1 in Science. He has never felt that the other subjects were less worthy, he just wasn't as interested in them. His least favourite subject is English and if it wasn't compulsory I'm sure he wouldn't study it at all! Having said that he stills excels at it but is not interested in taking it further and I don't have a problem with that.
Just from our personal experience, my son would not have been happy if he wasn't challenged sufficiently in his areas of strength and interest and this was certainly evident in his behaviour.
I hope this helps.
