Given past enrollment data, I wouldn't count on entry into the TAG program at GMS. Last year only 1 or 2 kids got in via the lottery.
The new TAG center at Tasker has had a postive impact on TAG lottery chances at Kenmoor and Tasker though. If you can manage the transportation, you may be able to get your child into one of those school. They allowed non-boundry kids to apply this year because they made it through their waitlists.