I'm debating over getting the older R171 or the newer but cheaper RP501.
R171 is listed as 10 stiffness index while the RP501 is 8, but it has boa dial and is the newer design and everything.
Can you notice between 8 and 10 Shimano stiffness index? If the stiffness is noticeable, I'd probably take R171, if it's not that noticeable, I might get RP501.
My only experience with Shimano is RP2 which is 6 in stiffness index, and it is a bit too flexy.