Bad choice of wording on my part - IAD isn't an issue as such, more so it's my closest/preferred airport, and only United use it as a hub. So I wondered if in reality I had any choice other than United. I'm actually 90 mins north-west of IAD, up in NW Maryland close to the PA line. It's much easier for me to go south from Frederick, down Route 15 and 7, and sneak into IAD without having to go near either Baltimore or DC beltways. That said, BWI is totally viable and acceptable as an IAD alternative.

Thanks for all of your other insight - some very useful info which I'll continue to digest and consider.