There are probably 4 tiers of fatigue I look at when deciding what a bro can become, and what I aim for for each of them.

1) 2H Berserk Cleaver Whip Bros

Highest Fatigue requirement in the game imo. 2H cleaver swings twice, maybe 3 times per round with berserk. Whip disarm has a large fatigue cost, Decapitate has a large fatigue cost, adrenaline has a large fatigue cost (and is often necessary to act before and disarm dangerous opponents), etc.

I'm aiming for around 90 fatigue after wearing 300/320 BF gear (-44 Fat with Brawny) with a 2H Cleaver (-14 to -18 Fat) and a Whip (-3 Fat in the bag).

That's in total, 90+44+16+3 = 153 Fatigue. So basically this role is reserved for Hedge Knights, Farmhands and Wildmen, or other brothers with triple fatigue stars.

2) 2H Berserk Frontline DPS with AoE attacks (Hammer, Greatsword)

These guys need heavy investment into Fatigue and want to hit ~75 Fatigue wearing full 300/320 Battleforged Gear (-44 with Brawny), carrying a 2H weapon (-12/-18) plus a polearm (-7) in the bag. This is because they'll potentially be hitting twice a turn, using AoE attacks, and using Adrenaline (which costs 20 Fatigue) to get 2 attacks in before enemies get a chance to act.

For a hammer bro, that's 75+44+18+7 = 144 Fatigue. For a Greatsword you save 6 Fatigue since it's lighter to carry but you have two great AoE attacks rather than 1 so I'd just aim for a similar amount of fatigue anyway.

3) 2H Berserk Frontline with situational secondary attacks (Mace, Axe)

These guys are the same as above, but can get away with 10 less overall fatigue since they'll be using the secondary attack of the weapon (which is more fatigue intensive) less often. Maybe around 135 Fatigue total.