[Boron]

A Theurg has 6 RP and costs 150 Gold , because he is sacred he costs slightly lower upkeep then a sage .
The nice thing is that a Theurg can be used in early-midgame as a quite good combat mage also and in lategame as a "fodder"mage .

A Seraph costs 100 Gold and gives at least 5 RP , so an almost as good researcher then the sage but also a very nice combat mage too .
Finally there is the generally more useful non-capitol only seithkona also .

All in all most nations really benefit from sages though and only for the 3 above mentioned Nations sages won't bring a big extra advantage , though you probably still build 1-2 sages even with these nations if you can afford .