mamash: Why not do the same as your Rov does (daven Ashkenaz when not at the amud)?
For one reason, I like davening everything along with the rest of the shule. Another reason is I personally just don’t like switching back and forth (I daven for the amud alot). Third reason is the Rav gave a psak that it would not be a problem. Fourth reason is the majority of Israelis daven Sfard. Last reason is I like the wording better – it makes more sense to me.
(A few months ago, I attended the morning minyan at a shiva house up the street several times to help make a minyan. For various reasons, I davened for the amud, and it was nusach Ashkenaz. After over 4 years of davening exclusively nusach Sfard, it was extremely difficult to go back to Ashkenaz. I had to literally daven with my finger on each word to make sure I didn’t mess up.)