I traded my Elgar Plus for the Scarlatti DAC this past, spring and added the Scarlatti clock (hadn't used a Verona clock) shortly thereafter. My Verdi had been serviced less than a year ago (including new optical pickup assembly) and the Purcell has never blinked, so it made more sense to me to keep those and move to a "hybrid" dCS stack given the price of admission.
Fresh out of the box, the DAC had me wondering whether I'd improved the sound, but within about 100 hours the Scarlatti VERY clearly outpaced the Elgar Plus in naturalness, low level detail retrieval and realism that has well-justified my decision. The clock was added so soon after the DAC that I cannot opine about their individual contributions. In fact, I added a pro audio Antelope Audio Rb 10Mz master generator at that time as well. At this point I'm simply enjoying my system as a whole and won't swap clock components in and out to assess effect, leaving that to reviewers or whomever.
Don't know if I'll ever find the Scarlatti Transport/Upsampler "affordable" enough to add in place of the Verdi/Purcell, but have no interest at present. I did just acquire a very reasonably priced, used "Upgrade Company"-modified Esoteric P70 transport. It's being serviced and should arrive shortly. Redbook and SACD sound so alike in my system with the Verdi that, with the dearth of SACD titles, it made more sense to try a well cared-for used, tricked out top Redbook-only VRDS transport which accepts master clock sync. I'll try to remember to post comparative results versus the Verdi, upsampling each via the Purcell. FWIW, the P70 also can upsample to 176.4 dual AES within the transport, giving another option without the Purcell in the chain- possible insurance if the Purcell ever fails.
My system is pretty unconventional, but sounds great with the Scarlatti pieces - REALLY great!
Hope this helps.