DiMarzio HS-2:
https://www.youtube.com/watch?v=VZruE7E_4OU
DiMarzio even recommends running the top coil of the HS-2 as an equivalent or near equivalent to some of their OEM single coils. The Steve Morse signature single is a split HS-3 (
link).
As for the Duncan stacks...
This forum is littered with reports that the split STK-S4 sounds just like an SSL-1. Combine this with the STK-S4 being slightly louder than the SSL-1 and you're home free. The -S4B is slightly hotter and the -S7 is another bump in level while still using the same type of wire.
...so yeah, I think there's something to splitting stacks.