i don't think there is a set amount of agi that increases your aspd in regular intervals that is universal to all chars and all weapons as you have to take the weapon a character is using and the weapon delay it gives and stuff.
i will try to calculate your aspd so lets assume you have 30 dex for the extra hit and are using an awake and have one doppel
ASpd = [200 - ((100-ImprovementPercentages)/100) * (WeaponDelay - ([WeaponDelay*Agi/25] + [WeaponDelay*Dex/100])/10)] is the equation you use and is quite simple to understand.
so with max agi we will have dex for the extra hit and are using an awake and have one doppel
ASpd = [200 - ((100-(30+15))/100) * (50 - ([50*99/25] + [50*30/100])/10)]
will mean you will have 184
im not sure what the average sin has as bonus agi but lets asume it's 30 as that is not unreasonable and easy to obtain
ASpd = [200 - ((100-(30+15))/100) * (50 - ([50*129/25] + [50*30/100])/10)]
so about 187.5 and we always round up so 188. i forgot to round in the previous one so it would be 185 not 184
ok this time 140 total agi and 40 dex
ASpd = [200 - ((100-(30+15))/100) * (50 - ([50*140/25] + [50*40/100])/10)] that would be 189 exactly
im not sure what the average agi/dex a sin could/would/should have but what i guessed seems to be not out of reach of most sins.
also if you add any more dex or agi after the 40 dex and 140 agi you will get like 189.01 aspd and as we always round up you will get 190 aspd. if you tell me your bonus stats from job levels and gears i could more accurately find your aspd.