Great effort Bob! I wonder whether we'll ever find those elusive baptisms.

I noticed that you had also considered Paddington. St Mary, Paddington Green also seems like a good contender, from my (poor) map reading skills, I think its quite close to Bryanston Sqauare.
Re: the St Mary Abbotts indexes, do you think they relate to funerals? They were listed as burial registers. I wondered if that meant the church had responsibilty for their burial. I have had contact with the archivist there, it might be time for another email to her.
The details for those (which were just handwritten records copied from the church records) are:
Martha Traies, 11th September 1842, age 48, Gravel Pits.
Art. Evans Traies, 22nd March 1846, 4 months, 2 Greyhound Row
Harriet Sar. Traies, 3rd March 1851, [looks like "birth"], Greyhound Row
Cheers
Sam