Granted these are different techniques, there seems to be a line where Pale Ales start to become more bitter and hoppy and IPA-esque. The thing is that Pale Ales don't usually list thier IBU on the bottle.
Hence the question; does anyone know about where Pale Ales end and IPAs begin, with regard to bitterness at least?
Referring to the BJCP Style Guidelines, the following is true:
English Pale Ales (ESBs): 25-50 IBUs
American Pale Ales: 20-40 IBUs
IPAs: 40-60 IBUs for English, 40-70 IBUs for American, 60-120 IBUs for Imperial IPAs
Based on this, the answer to your question should be in the 40+ IBU range to differentiate bitterness between pale ales and IPAs.
Bear in mind these are guidelines and not gospel. Generally, the BJCP style guide is a great starting point.
Geeks Mental is a community that publishes articles and tutorials about Web, Android, Data Science, new techniques and Linux security.