Its complicated now due to the fact that any form of slow will also lower ur fpa.... So you kinda need to stack for golem slow, decreap, holy freeze, impale, arach, gleglaws, blackhorn's and div wepons with slow.
The 4fpa breakpoint is 41 EIAS.
Eias = Floor(120*IAS/(120+IAS)+SkillIAS-(WSM)-GearSlow-SkillSlow-ChilledSlow
The formula for fpa is:
1 handed weps and 2 handed swords: RoundUP(7*256/floor(256*(100+EIAS)/100))-1
2 handed weps: Roundup(9*256/floor(256*(100+EIAS)/100))-1