Hi gmat7294,
If you're dead-set on retesting, with the goal of scoring closer to your practice CAT scores, then there are a variety of other factors that you have to think about (regarding how realistic those CAT scores were relative to your Official GMAT score. Here are some things to consider:
1) What did you do in the 3 days before your GMAT?
2) How did you sleep the night before your Test?
3) How long was the ride to the Test Center from your home?
4) Were there any distractions at the facility or during the Test?
5) What did you do during the two 8-minute breaks?
6) Did you finish any sections early or have to rush to finish any sections?
Etc.
At your scoring level, all of the little details matter - and some of them are things that you will never have any control over. This is all meant to say that you certainly have the necessary intelligence to score at the 770+ level, but you'll have to keep all of the little mistakes from happening during the Exam AND you'll have to make sure that you've properly accounted for a variety of non-Test variables.
GMAT assassins aren't born, they're made,
Rich