I have listened extensively to the SP-10 mk 2 with nos tubes in my system. I currently have a CAT SL-1 Mk 1 which is of the same vintage as the 10. Both are excellent pre-amps and were compared in a mid 80's Stereophile along with the SP-11 by Anthony Cordesman. I always preferred the 10 over the 11, just a preference in presentation.
There is something quite magical in the midrange with the 10, great bloom and stage depth that is hard to resist. With an upgrade of better parts from Steve Huntley (I spoke with him a while back and he was using a highly modded 10 as his reference) you can't go wrong. One area it definitely separates itself from the CAT is the phono stage which is just as good as everyone above notes and the CAT is no slouch in this area. I would definitely consider the 10. Also of note is that tubes are critical for this pre.
There is something quite magical in the midrange with the 10, great bloom and stage depth that is hard to resist. With an upgrade of better parts from Steve Huntley (I spoke with him a while back and he was using a highly modded 10 as his reference) you can't go wrong. One area it definitely separates itself from the CAT is the phono stage which is just as good as everyone above notes and the CAT is no slouch in this area. I would definitely consider the 10. Also of note is that tubes are critical for this pre.