Please post your bike model, height, stem length, and frame size:
Model Dogma 2 BoB
Rider Height: 6'1"
Frame size: 57.5
Stem: FSA 120mm
It does not sound like the other person is a racer so the 56 with a positive stem would be the ticket.Hi
I had the same question as you being 6'1" 560 or 575 but I went with 560 after studying
stack and reach measurements.
I have a BB-seat height of 81cm and require a 1cm spacer the make the drop to the bars comfortable.
So to answer your question, if you drop a size your saddle will be approximately 4mm further back. So hardly noticeable in terms of aesthetics and if you use 20mm or more of spacers with the 575 frame you may need to run a positive angle stem or use another 15mm of spacers which would be nearly at or just over the limit for the frame (someone will confirm).
Hope this helps your decision.
57cm frame and 80mm stem? Expect very twitchy steering. Definitely not relaxed handling.
Can you try a Rokh? If not go for the smaller frame and a stem that angles upward.