Hi maliyeci,
First off, a 740/Q49 is an outstanding score (it's well above the 90th percentile overall), so you should apply to any Business Schools that interest you. As such, a retest is probably not necessary. You're ultimately asking Admissions questions though, so you would likely find it beneficial to speak with an Admissions Expert about your overall profile. There's a Forum full of them here:
ask-admission-consultants-124/PhD Programs tend to be highly competitive, since there are so few spots, relative to the number of applicants. If a particular Program requires a Q51 for admission, then I would be surprised. However, you should be able to contact the individual Schools and ask.
GMAT assassins aren't born, they're made,
Rich