Inspired by this comment
Assume that a particularly deranged moustache-twirling villain with way more time and resources than is reasonable decides to build a satellite-launching rocket using chlorine trifluoride. (Never let your moustache-twirling villains get bored.)
Assume the ever-so-trivial engineering problem of actually building and launching the thing has been solved. Somehow.
With any choice of propellant, as long as it isn't even less usable than chlorine trifluoride (arguably an easy criterion, as long as you aren't using pre-mixed methane-oxygen), what could, at best, be its performances? How would its Isp and thrust compare to sane engines?