Never got to hear the ARC Ref. 3 pre-amp, unfortunately. It was for sale used on consignment...I would be interested to hear it some day though. There seems to be a solid chunk of audiphiles who believe strongly in pairing tube pre-amps with solid state amps!
I listened to the Mac C50 pre-amp and the MC452 amp (all solid state Mac gear). I did hear the Levinson/Usher gear in the same room and on the same speakers (Revel Ultima Studio 2s) as the Mac gear (same CD player - a Levinson - and cables too). I found that the Mac gear had a different sound that I'm used to from my current Simaudio gear. The Levinson/Usher combo was closer to the Simaudio sound.
I perceived greater "soundstage depth" and "space" with the Simaudio, and particularly the Levinson (the pre-amp threw a huge, deep soundstage wheras Simaudio is a tad more forward) gear whereas the Mac gear sounded more "direct" with more "body" or "presence" to the music but less depth. Tough to describe in words but you'll hear a significant difference if you do the comparison.
Funny, my Simaudio dealer sells both Mac and Simaudio and he said "If you like Simaudio, chances are you won't like Mac." - it comes down to what you prefer but the two brands are quite different in how they present the music.