agree with @
Bacciagalupe, position setup is gonna make the key difference.
maybe compare to what you currently are riding, the Scott Cr1 and the ROubaix in same sizing, using Bike Insights and/or Geometry geeks. And then compare to the 56 Roubaix.
If you compare on Bike Insights, you'll get a visual comparo - which can point out similarities and diff. in geometry.
The 2 big diffs which stand out are Stack and BB height. BB Height of the CR1 is on the high end, typical for real race bikes which might be used for circuits with lots of turns/corners - Crits. The High BB allows a bit more lean angle clearance before possible pedal strikes (if one needs to pedal through corners...) But Higher BB also moves the CoG/CoM higher, which feels a little less stable at speed.
Maybe consider how you're currently positioned on your CR1, and what you want to change and what to keep. Once you get your saddle positioned, then its Stack and Reach. Ultimately the Roubaix in 54 starts out at 20mm higher stack than the CR1, How much further you got then depends on the stem angle and length (and spacers...)
The ROubaix will 'feel' different on the road, compared to the Scott, but that will shake out after a ride or 2. Or maybe not... You'll only be able to know, once you get some time on whatever you choose.
If you are in analysis and decision paralysis, and 'stack seems to loom large on the decision - you could buy an adjustable stem (at least 1, maybe 2 cm longer than current stem) and just try different angles which will give an effective 'stack' to compare to your current setup. - There are reasons why the adjustable stem should be longer,,, for testing...
I have Roubaixs and Tarmacs, but what and why I have, size-wise shouldn't be a consideration for anyone else. Most everyone considerations might be quite different.
Ultimately, getting on a bike, even for a short ride around a block, helps... If you do get to ride a Roubaix, bring your Scott along and ride it on the same section - compare...
And if you're buying a complete bike, as opposed to frame and parts, then what is hung onto the bike may have as large an impact.