I have owned ARC preamps and currently have the CAT SL-1 Signature. IMO, the CAT is superior in terms of presenting the sound stage, the space around performers and in overall resolution. Even though it's tubed, it does not have what you would call "tube" sound - the entire audio spectrum is presented with pinpoint accuracy without coloration or emphasis on or at a particular area. For opera and classical music, it's practically a must.
The ARC preamps were, to me, excellent sounding with slightly more punch and definition in the bass - I absolutely loved my LS2B MKIII - however the CAT is (to me) preferrable in many respects. In tonal balance, and musicality, I found both ARC and CAT's are very similar. Since you have the VT100's, you may very well prefer ARC for the sound and synergy ARC equipment has with each other.
But if you are considering a CAT, many have called it one of the best preamps you can buy at any price - and you can upgrade around it with practically anything on the market. Just keep in mind that CAT's are single ended; probably the biggest reason why they are not as prevalent for a product of this caliber. Of course, this is MHO from the standpoint of my system, room and music preferences.