I prefer
Ignatius. I think
Ignatius is handsome. It's a "big" name but it's strong and
Iggy is a fun and approachable nickname, even if you don't personally use it (others will though).
I like
Percival much more than
Percy and unfortunately, being the '
Harry Potter' generation (as in you and I and some younger and older), I think many people may associate it with
Percy Weasley. I do. I don't know what I thought of it before HP but I think
Percy sounds so weak and sniveling and creepy. I don't love
Percival but I think it's far and away better in it's full form than
Percy.
I like your personal connection to
Percy though- so I'd go with
Ignatius Percival Stewart if I had to choose. For me, it keeps the handsome sound of
Percival and avoids negative connotations some may have with
Percy as a nickname and the flow is really nice. Obviously, just what I would choose- whatever is comfy for you and
Dave is most important. But I do think you'd be picking a name that is fairly widely actively disliked if you went with
Percy- whereas some of your other more old-fashioned and unusual names that are to your taste would have people going more "Huh..." and then they like it because they don't have a strong association with name except "old". I hope that makes sense?