Dervy! Welcome back! Here, have those BLM numbers I've been promising! Alas, due to limited gear sets I wasn't able to get my Determination very high like you were asking.

51 WD, 493 INT, 294 Determination 50 potency (Blizzard II)
Non-critical 98-109, critical 148-163

51 WD, 493 INT, 294 Determination 100 potency (Fire II)
Non-critical 198-219, critical 298-327

51 WD, 329 INT, 324 Determination 50 potency
Non-critical 70-77, critical 104-115

51 WD, 329 INT, 324 Determination 100 potency
Non-critical 141-156, critical 211-233

And a "full gear" set:
66 WD, 508 INT, 301 Determination 50 potency
Non-critical 123-136, critical 185-204

66 WD, 508 INT, 301 Determination 100 potency
Non-critical 245-270, critical 367-406


So, umm. . .why are the 100 potency numbers not 2x the 50 potency ones? >_> I could understand 2x+1 due to rounding, but the crit values on the second set are 2x+3. . . and then the third set are actually less than 2x the originals. I'd like to think that the 50 potency crits on the third set are supposed to be 184-204, but the game refuses to give me a 184 crit despite hundreds of crits. . .so yeah.