I found Fiasp the same strength as NovoRapid except when my BG is high.
For me, Fiasp speed (and to a lesser extent potency) is very very dependent upon my current BG
If my BG is in the 4s, it works instantly. I have to bolus AFTER eating to avoid a hypo.
If my BG is between about 5 and 8, 9 can bolus before eating.
If my BG is higher, I need to prebolus.
If my BG is in the teens, it's as if I am bolusng water. It can take an hour to move and then plummets due to my rage bolusing.
Compared with NovoRapid, I need more care to avoid the higher numbers.