Sizing BMC TMR01

[IAMBOB]

I want to buy a TMR01 Road Bike (no dealer near me) however, I looked at the geometry and I am very confused. Are these bike bigger in size?? Every bike I have ever had is a 54 which fits perfectly (currently scott cr1), however when I look at the numbers for the TMR01 road bike it looks like I am more suited to the 51. I am 175cm with inner leg 80cm and smaller arm span at 172cm. So am I a 51 or do I just go with the 54?? Advice would be great as I have to buy online because I am miles away from a dealer.

[flex5150]

Im a 54 in most bikes but a 51 in BMC, going by your specs hit the 51.