I just did some testing of Ukko's Fury pre and post nerf.

Pre~100% | Pre 300%
Min 831 | Min 1663
Max 3277 | Max 3306
Avg 1973.3 | Avg 2789.2

Post~100% | Post 300%
Min 1374 | Min 1670
Max 2687 | Max 3223
Avg 1780.2 | Avg 2356

~9.8% dmg drop at ~100% TP
~15.5% dmg drop at 300% TP

This test was done on Lesser Colibri, wearing full Empyrean+2, Goading Belt, Heed Ring, Rajas Ring, lvl90 Ukonvasara, Pole Grip, Atheling Mantle, Brutal Earring, Ravager's Earring, Ravager's Orb, Agasaya's Collar. No /ja were used.