I wouldn't say they are elite but the Tylmai are crystallurgy. It's an ok AI if you give them bonuses and in late game they know how to be sneaky
Oleg's Tholians are a tough challenge, very good AI, well against me anyway
It's a modified Version of the Tylmai, or at least i think as the games i've played in it's been superior to them.
Lastly Andres Lescano's Y'Gathian Free States are a very good race too, even with no bonuses they practically overwhelm you with well designed ships, they also have the organic manipulations tech tree as well so they might not be what you're after!
Hope this helps
