The traditional pencil and paper, 8 hour, two part FE exam has just finished its final iteration. Starting in January the tests are now 6 hour, more discipline specific, computer based exams.
I still believe it's up to you as to whether you choose your own discipline or the other disciplines version. If you are still allowed to choose the other disciplines (which I suspect you can), then it will still not hinder you as far as your career is concerned. My first suggestion is to read through the topics for both the chemical and other disciplines versions of the tests. These are available on the NCEES website. Then determine whether you'd even be more comfortable taking the other disciplines version. I personally took my discipline specific version (mechanical), because I didn't want to have to review/learn some of the topics on the other disciplines version. It was much easier to do more/harder material that I have continually covered in my curriculum vs studying material that was either not taught or quickly forgotten.
If you then feel better about the other disciplines version, then you can verify that you are allowed to take it. Again, my thoughts are that it's up to you, but I don't see it posted for certain either way under the description of the completely new test that you will be taking. My suggestion is to make sure for yourself because if anyone offers advice based on what they have previously done, it might not apply to this new test.
Your best bet is to realize that there is no "tougher" version. It is all relative to what you have done, can successfully do, or how you would like to study for the exam. For myself, I was allowed to use my score (TBPE provides an actual normalized score, regardless of what NCEES says about not providing any scores) to replace my final exam grade in my capstone courses. I worked very hard for the test, and after taking it, realized how overprepared I was in the case that I was simply trying to pass. I would have said that simply being proficient in my previous coursework, and maybe some slight refreshing, was more than enough to simply pass the exam.
Note again, that my comments are based on the old test. There is no metric yet for the new one. Best of luck.