It seems to me that giving both Slann the same lore is something of a waste. While being able to cast a hex twice is nice, I’d think that you’d be able to get a lot more by gaining access to more spells. For example, using the lore of life and the lore of light together would allow you to cast earthblood, awakening of wood, flesh to stone, throne of vines, shield of thorns, the speed of light and Birona’s Timewarp all in the same turn due to their low casting costs (which allows to capitalize on your rumination). Sure they’ll counter some of it, but you can be sure getting off some excellent augments. Seeing as your fairly determined to play a single large unit of Saurus, I think it may make more sense to use augment spells rather than hex spells (after all, if you only have one unit, giving them +4 T is just as good as giving every enemy unit -4 S (apart from the armour piercing bit) and it’s a hell of a lot easier to cast a single defensive spell on the unit you want to protect than to cast hexes on every enemy unit in charge range). However, if its working for you, you probably don’t need to change it.
Despite their infinite wisdom and intricate knowledge of magic, the old ones failed to foresee the purple sun of Xereus.