Dunno, but you've always reminded me of what I think my dad must have been like when younger, and if he were actually into foruming and didn't scoff at mbti!

I've recently decided my dad is an IxFJ -- and rather lean towards ISFJ, as he is very deliberate and on top of things and reasonable and not driven to flights of fancy. He's extremely intelligent and didn't have an FJ-type career at all (ended up being a senior economic analyst), was in the navy, is very much into reading/learning about history and watching all of those history-type and war-related shows on tv, and reading about all of that and educating himself. Also into science. He loves to learn. He has a great memory. His church life and volunteering has become more important to him as he's gotten older. I think he has a strong sense of honor and of 'doing the right thing' in life, and being a good human being. For the longest time I thought he was a T but in hindsight that makes me laugh, as he has a lot of Fe. It's just that male versions of Fe and ISFJ/INFJ can be quite different from female versions.
Sorry I went and started talking about my dad! Bottom line is I don't know you well enough to make the call. You strike me as walking a slightly different line from other INFJ's on here...something about your thought processes and the way you present things...but that honestly might not mean a thing, as there are many flavors of INFJ's to begin with and I could say that about a lot of them on here, including myself.

Maybe something to look into and explore - you'll either decide you are in fact ISFJ, or you'll decide there's no way in hell you are, and you're INFJ like you thought all along! ;-)