Hi, based on your description, a 54 cm would be the right size. I have been riding a 2018/2019 R5 in 56 cm. I am 6’0", 32/33 inseam. I rode a 56 R3 (2014) before. The 56 is perfect for me. I run a 110 cm stem, and the zero offset seatpost. The stack is lower than the R3 (2014) I used to ride, but there’s also slightly more tire clearance on the R5, so the fork might be a few mm higher (I’m not sure about that). I have 20 mm of spacers under the stem.
Also building a 2019/2020 R5 for my wife. She’s 5’7", former pro racer, long legs/femur with ~31/32 inch inseam. She went with the 51 cm, but to get the stack she wants, needs more spacers (25-30 mm), and will probably run a 120 mm stem (angled up) and the 25 mm offset seatpost to make the reach long enough for her (the size 51 comes with a zero offset seatpost, while the size 54 and higher comes with the 25mm offset seatpost).
Anyway, the R5 is awesome – really snappy acceleration and stiffness in the BB, along with comfort on longer rides (after 2,000 miles on mine since since building it earlier this year). Feels much more responsive than my 2014 R3. Happy to post a photo or answer other setup questions.