Profile Evaluation

Hello Experts

Thank you for your time in advanced.

First Let me introduce myself.

I am a Mechanical Engineer with 8.5 years experience in Product Design. (Design of metro Trains & high speed trains )
Currently I am working in UK for Bombardier Transport, Derby as a Work Package Leader for the East Anglia train design team.
Professionally, I have taken up some challenging jobs & have some significant professional achievements (Bagged a multi million dollar project last year for QUEST global, Crucial in developing talent pool in rail domain for QUEST Global, Have been awarded more than a dozen times in my career for performance, Experience of handling client from 5 different nationalities, Worked from client locations for more than 4 years of my career including 1+ years in UK & France)

I have a below average academic background.10th (83%), 12th (49%) & Btech (63%).
I have a GMAT score of 690 (Q50, V33, IR6, AWA 5).
Considering my poor academic background, I am planning to retake GMAT in order to give myself a fighting chance. But due to work pressure I am unable to devote time for GMAT prep.

Any Data or information on these below questions will be immensely helpful to me in order to get a clarity.
1A. I need an insight on how much a below average academic background such as mine can hamper my chances at IIMA,B & C? 1B. What is the acceptance rate at these schools?

2A. Schools that I will have a good chance with GMAT 690? 2B. What is the acceptance rate at these schools?

3. Considering my poor academic background, is a GMAT score of 750+ is must for me or do I have a fair chance even with 690?

4. When Should I retake GMAT if I wish to apply this year? (I am thinking OCT last week)?
Regards
Alok