Shivans seem to have much more powerful reactors...were any Shivan capital ships ever definitively captured and analyzed? I know that the Taranis was captured, but was destroyed at Tombaugh.
If Hall Fight is canonical, then an Azrael was also captured, but the boarding party was slaughtered. Depending on when Antares fell, that may have come to nothing as well.
Anyhow, the weaponry on the SC Lilith is a pretty good indicator of their reactor tech...LRed on a cruiser? Along with Shivan AF beams and, IIRC, a pretty good speed, that far outranks any Terran ship.