Looking at Xietor's comment, wishing was definitely the way to go from S5 onwards. S5->S6=90 gems, and with the Sea Father site Wish=80 gems. Having at least 5 in all paths might be pretty good for Strands of Arcane Power, as a fringe benefit.
I use the 24 research pretender combined with those Oreiad's, philospher's don't do enough research per turn. OK they may be cheaper but I like to set up the pretender and 4 or 5 Oreiad's doing the research,then I make a mage/enginner and make quill pens for all of them.
The pretender has 7 dominion, sloth 1,growth 1, lev 2 in all magic paths except blood. Seems to be working well when playing the AI.
Oreiads make quite respectable thugs. Stick a horror helmet on them..