I am also wondering if for the Scheckter the Cold Sweat or Miracle Man would make sense. Especially the MM lives from that low mid punch plus the highend, with the midrange there, but not the focus point. Might keep it from getting muddy and deliver a lot of balls to the wall. The Coldsweat moves along similar lines, but is lighter and a bit more old school.
I do not know however exactly how they would handle these tunings. I recond it should be ok, I mean for a 7 string it technically is like drop D. The should deffo sound less shrill and ceramicy than SD pickups, plus much more defined and open.
Additionally I would throw the Rebel Yell in the ring. Tight, punchy, and with such tunings and a proper amp it should deliver all the balls one should need. As a member of the League of Ordenary Gentleman myself I would say this might actually be the best pickup here, given the right amp. The Protest sound is suprisingly middy and the RY has a rocking upper mid spike that will get you up front. High end made up of harmonic overtones and a punchy bottom. With a modern metal sounding amp it can absolutly nail that style (Red Seas Fire demonstrate that too). Also loves 7 strings because of the awesome definition.
So maybe MM or CS, but most certainly RY. Got it in my Protest signed Ibanez S and daaaaamn in a modern amp (not my Tiny Terror) it can nail that sound...well if you can play like them too, which I can´t even begin to. ;)