I've found Phantom mode to work great when you don't have an equal quality center, but when you do, a center speaker really "locks" in the center. Revel makes a big deal out of timbre matching, which they claim does not mean "exactly the same as R/L". Try listening to a Revel Voice or [cheaper] Performa C30 to hear how good a center channel sounds.
Is the center the center ??
I have seen interesting discussions about center speaker quality and matching to the main speakers. That would speak for a set of speakers from the same manufacturer. Unfortunately the manufacturer of my Audio Physics main speakers does not offer a center speaker, so I have to find one from another source (The ProAc Response CC One I use currently is not bad, but I have heard better ones.). If the price is not the main factor is the Nautilus HTM1, the Aerial CC3, the Legacy Audio Silverscreen (model II, approx 1.5 k$ ??) of the Martin Logan Theatre THE center speaker for my system? Are there reviews of center speakers available (Stereophile apparently does not review them.).