In my experience, I've seen no difference in ranking for keywords between a shared and dedicated IP.
Other than that, your question is a little vague.
How much bandwidth are you currently consuming?
Large databases? Any CMS, forum, tube scripts and if so, the size of them?
Streaming videos? If so, what size and roughly how many, (not exactly how many, but 50, 60 or 10,000)?
Are you a program and/or paysite owner?
Depending on your situation we can properly assess which solution would be best suited for you.
