@User when I looked at the options a while ago it seemed to me like the 3.4 x 3.4 PNP is optimized for bandgap purposes. Looking at the info on the read the docs pages the tolerances are much tighter than any of the other bipolars. Originally I was going to use an NPN to avoid the substrate minority carrier injection from a PNP but the limits of the 3.4 PNP made me go that way instead.