Nordost Blue Heaven to SPM Reference

Nordost cables are known to be very detailed, quick and having a fast transient response while their only caveat is in the bass department. Anyhow I don't think this is an issue with me since I am thinking of improving the bottom end of my speakers with a subwoofer.

I have the Blue Heaven speaker cables on my SF Grand Piano and was thinking of upgrading to the SPM Reference. Will I get a substantial improvement? I am just concerned on the ratio of money spent/improvements in sound. If the differences are huge I don't mind getting rid of my Blue Heaven for the SPM. Any comments?

Thanks in advance.