As always building lists with the idea of taking on all comers(yes there will be tough matchups, Saeryn comes to mind)...
The idea is stacking +hit and +damage throughout the army. The Mauler can buff the Axer and vice versa. Even the Cronicler and KSB can put out respectible damage in light of each others buffs and eMads Vortex of Destruction. Axers, Champions and Fellcaller can double duty against both fodder and armor. The main weakness will be anything that debuffs speed such as Breath Stealer.
I would think you would take plenty of advantage of some stuff with reach, like Mulg, Long Riders, or a Hero. In this case, a Hero would serve you better than a Fell Caller since the fighting part of your army is already plenty accurate, and you have Killing Ground for terrain negotiation.
Fell Caller is more than pathfinder or +2 to hit. 2 Attack weapon master, accurate spray and stand up for everyone KD.
Still the +2 is nice when looking at high DEF casters or models with a DEF buff like Defenders Ward or Iron Flesh.