Hi and thanks for your question.

I'm afraid that there is no single answer to your question. There is no "safe score" since, as you probably know, there are lots and lots of factors that go into an admissions committee's decision.

But...to answer your question: to be competitive at the programs that you mention below, I think you would need a minimum of 650, and possibly even higher since your GPA is not particularly strong in either grad or undergrad.

A few other notes:

Given your computer science background, I would imagine that you should be able to fairly well on the GMAT. Many times, people with strong quant backgrounds do not do well b/c they are not familiar with what I call the "core knowledge" --the triangle ration, the standard formulas, etc., etc. Similarly, some basic knowledge of question types and strategy is often very helpful.