I will say, when I looked into and applied for IBR (I had $50,000 in loans and was only making $34,000), I found it didn't help me. This is because, like the OP, I had a mix of federal and private loans (oddly my private loans are the lower interest ones). Because I only had $30,000 in federal loans, my IBR payment was only a little cheaper than my normal one.
Now, I did not apply for any of the options that change the loan term from 10-years, obviously that would have a bigger impacts. Also, I was still eligible, but I'm guessing I was on the cusp since it didn't drastically change my payments.