INTPs will end up with extremely abstract theories that the usual ISTP will think is a little insane. ISTPs are more driven to test and play around with these ideas and if they don't quite align with reality they will be quicker to reject them. INTPs will entertain ridiculous ideas like ENTPs do but they will be quicker to narrow them down and see if they have any truth. It doesn't matter if these theories don't appear to be in the real world, so long as they can be mentally understood they will have some acceptance by the INTP. They will be content until information begins contradicting their models where they start all over again.
ISTP 5s will appear even more like INTPs, but I think their thoughts tend to be way more concrete than INTPs.