For the record, for the way I play, 7d+1d would probably result in longer games on the average. I'm probably someone the fast-paced players would find frustrating to play against.
I probably go about a move per day and occasionally play through variations ~quickly. However when the move is complicated - taking lots of reading or evaluating value of multiple feasible positions on the board - I will often take my time. That means I would alternate between filling in the max clock time and spending it.
With 3d+1d I only have at most 3d to waste considering a move (I don't really spend all my day thinking of the move ofc, but I do come back and take a look 1 or more times per day). With 7d+1d I would have 7d to waste.
(Personally, I would be super happy with 7d+1d, I've come close to timing out games during busy periods as well as others on this thread)