Interesting. I can’t advise, but some thoughts:
One can use contactless at Maidenhead, which I presume is cheaper than paper tickets. No idea how you would (elegantly) obtain a contactless extension, though.
If you swiped out with contactless having swiped in with Oyster then it seems likely you’d be charged a maximum fare and would be entitled to a refund, but it seems plausible you’d technically be travelling without a ticket once you got to zone 3. I wonder what fares would be used to calculate the refund.
The TfL journey planner suggests GWR from Paddington for the quickest journey.