Having owned the SP8 and 9, my thoughts.
SP8 is complex and wonderful. I still have one. Retubing is no (economic) joke, however. On the SP9 you will want the MkIII. Cleaner all around. I had my MkI upgraded to III and really appreciated the difference.
SP10 and 11 have a lot, I mean a lot, of now very expensive tubes.
The SP6 is just too old, beloved though it may be. (IMHO) (But isn't everything?)
That being said if I needed a pre, the REF3 would be it. Absolutely gorgeous in every way, and a thoroughly modern design. Drool worthy.
And don't underestimate the seductive power of a remote.
(At the moment, I'm happy with my Moon 390 and listening to SACD's at 176.4 over hdmi. Not DSD, but not a million bucks, either.)
Just my 2cents.
Good luck, have fun and buy what makes you happy. They're all good choices.
(Oh, and I owned a Classic 60, and I'm still using a VT100MkIII with its 8 glorious 6550s. Yes, 8. Warm!)