Hmmm

If the stock shock is so good then why did HRC see fit to make a special one?

The HRC shock as a bit like Business class on a plane. Once you've been there, there's no way you'd ever want to sit in cattle class again!

Standard suspension is OK for most conditions, but anyone who's ridden with an HRC shock (or similar aftermarket) can surely vouch that there's no comparison.

Having said all that, the SP shock will definitely improve your setup possibilities over the R shock.