PNL has better proc for sure, but it has lot bigger icd. It may happen that it procs when you need to move or can not attack boss at all (marrow, rotf, PP, BPC, BQ, sindra..) and even if you lose only 3 sec of dps it will be higher lost than with dfo proc.
About getting SF to 1sec, there is a way, but only for 12sec. With all haste boosts (totem/aura + hero) still need 2319 as we saw before.
You say this gear gives 1585 + 240 (spellstone) + 170 (DFO HC instead of PNL HC) + 340 (engineer Hyperspeed Accelerators or 500 speed potion for 15sec) = 2335 haste
(or 2335 + (500 - 340) +45 (elixir)= 2540 and bring Sb to 1sec)
Of course only with hero/bl on -35% phase and if your accelarator isnt on cd;)

