Excuse me...
why the stop at conj3?
You don't really need more firepower to cast evoc2 battlespells with your mages imho.
You can of course use it but if you really feel rushed to get to constr 6 I'd rather suggest to take that stop
after const-6 or even after evoc-4 (for the firepower needed for fire cloud and then falling fires at evo5)
I'd rather suggest thau-2 before taking const, - you can actually start remote site searching so you don't need to stop your expensive armies for the search, but just a salamander in the cap (iirc), so you can alchemize more and have more gems for when you reach const-4/6