Question special

I understand that in general, it is preferred to have letters of recommendations from mentors in the same specialty as the one you are applying into. However, for example, let's say I have a particularly strong relationship with a pulm-crit attending that I worked extensively with in the ICU, but I am applying into gastroenterology. If I felt that they could write an exceptionally strong letter, would it be beneficial to use that as one of my letters? Or would I be safer using a letter from someone within the field I am applying into that may not be as strong.