Without reading any of the thread, I'm just going to give you a big old "YEAH!! GO YOU!!" for the topic itself.
Okay, I've read your message now, and I happen to have read the chapter on acceleration in my gifted ed textbook last night, so I flipped back through and found the following for you:
The current research-based consensus is that in most cases gifted students are quite comfortable with their intellectual peers - older students - and suffer no noticeable maladjustment.
For example, among Terman's gifted children, those who had been accelerated 1 or 2 years made better adjustments than those who were not. Brody and Benbow found that accelerated high school students did as well as, or better than, the others in all areas of achievement, had higher career aspirations, and attended more select colleges. There were no differences in social or emotional adjustment.
Gifted children, on average, are better adjusted socially and emotionally than typical students. However, children with very high intelligence have special problems relating to others because of their differentness. Because these children are the ones most likely to be skipping grades, their social problems, actually related to their extremely high intelligence, mistakenly may be blamed on acceleration.
Teachers and parents should recognize that keeping a highly precocious child in an unstimulating environment is also making a decision - one that communicates to the gifted child that he or she is not expected to perform up to his or her capability and that social success is more important than academic challenge. That decision can be more intellectually, and even socially, harmful to the gifted child than the decision to skip grades.
The book is Education of the Gifted and Talented by Davis, Rimm, and Siegle. Here's a list of some of the research they cited; maybe you can find one or two on Google Scholar and arm yourself with them.
Benbow & Lubinski, 1997: Intellectually talented children: How can we best meet their needs? In Handbook of gifted education (2nd ed).
Kulik, 2004: Meta-analytic studies of acceleration. In A nation deceived.
Kulik & Kulik, 1984: Effects of accelerated instruction on students. In Review of educational research.
Rogers, 2004: The academic effects of acceleration. In A nation deceived.
Southern & Jones, 1991: Objections to early entrance and grade skipping. In Academic acceleration of gifted children.
Terman & Oden, 1947: Genetic studies of genius: Vol 4. The gifted child grows up.
Brody & Benbow, 1987: Accelerative strategies: How effective are they for the gifted? In Gifted child quarterly.
Delisle, 1992: Guiding the social and emotional development of gifted youth.
Gross, 1993a: Exceptionally gifted children.
Rimm, 2007a: Keys to parenting the gifted child (3rd ed).
She is going on the trip of a lifetime (I'll mention that in another thread).