I believe from reviews and seeing people use them:
The Siege is a heavy ball, with its stock surface for the average revs (300), average ball speed bowler.
The Mission is a medium-heavy oil ball, with the same provisos as the Siege.
The Plague's intent seems to be to emulate the Virtual Gravity's general ball response, an almost flip type of backend on medium-heavy oil conditions. Both BTM and BJI have given it pretty decent reviews, with both sort of agreeing on the backend, but BTM giving it stronger overall hooking (medium-heavy oil) capabilities and BJI saying it was more for medium oil. I have not seen the Plague in anyone's hand's yet, Barry.
For whatever it's worth, keep in mind that the Plague is part pearl, part solid, somewhat like the Rogue Cell. (Not a 50/50 split)
So you could be putting a marker in the sand, so to speak for its overall hook capabilities.
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"None are so blind as those who will not see."