VPI JMW-9 to JMW-9 SIGNATURE upgrade pros and cons

I am considering doing this upgrade at a cost of $620 all-inclusive. I would love to hear from anyone who has made this upgrade and their listening impressions, both good and bad and whether or not it was worth the $620. (I have set up my TT level, aligned the cart with a Mint LP protractor (highly recommended to me and now by me), tweaked my loading, set the VTA, Azimuth, set the tracking, and set the VTF. If you have a Zyx Airy 3 I would like to know if the Signature arm tames the EXCESS sibilance (as apposed to the natural). My TT is a Scoutmaster with the ring clamp and a Zyx Airy3 cartridge.
Thanks 'Goners for your help...