MK: Just to clear up any confusion: I don't know/didn't care to find out. If there is one place that can shed some light for your query, GameFAQs is the place. As a bonus, you can probably find out how much Fury increases LB-gauge increments.

*Gets an Idea* Hm... You know... if you have FF7 PC available, it gets a bit easier. You can download a savegame-editor, save and stuff, give Cloud Omnislash and set it as the active LB, then load the game. Fight a battle or two (without Fury seems to be best for your purposes), carefully note how much damage Cloud takes, then save and exit. Open the save in the save-editor and see how much the Limit Gauge-number has increased (0-255). Wiggle some maths at it, and you should have a good estimate in no time.