TopGun,
Considering you are applying for European universities, 660 with 6 years exp is very competitive. It is equivalent to somone who is having 720+ with 3 years of exp.
You can still get into IE/ESADE/Manchester business school/Oxford Said School/HEC Paris/.
Had I been at your place, I would have gone with this score. There is no surety that you will get into these B-Schools even if you get 720+. All that matters is an amalgamation of decent gmat score, good academics, good no. of years of exp, involvement in extra curricular activities and a "can-do" attitude. These things should be reflected in your GMAT essays that you will be writing for each university.
All the best. Nothing to afraid. Go ahead with your applications. I have seen lot of people getting into these schools with 640-650 with 3+ years of exp. University will not rule you out just because you have 660, what puts you at par with others is the years of exp that you have. Let me tell you honestly, there are only 10-15 percent of people in each university with over 6 years of exp. Each university wants people from different domains and experiences.
All the best for your applications.