Footsteps of the divine says you can expend the spell to add "...an additional +10 feet to your speed per round remaining in the spell's duration." Therefore, you gain a bonus of 10 x 10 x 60 x 24, or 144,000 ft/round. Times FIVE for the Run feat gives 720,000 ft/round, or 120,000 ft/sec.
To put this in perspective, this hypothetical cleric is running at more than four times Earth's escape velocity. He's running so fast that an atomic clock could detect the relativistic time dilation he undergoes as he moves. He's running so fast that, if this weren't magic, his body would be torn apart as he instantly accelerated to 100 times the speed of sound.
By strict RAW, I think this is legal. Persistent Spell states, "Spells of instantaneous duration cannot be affected by this feat, nor can spells whose effects are discharged." Since footsteps of the divine (the spell in question) has Personal range, and its duration entry is "1 round/level" rather than something sensible like "1 round/level or until discharged", it would seem to be a legal target for Persistent Spell. (DMM: Persist is also not required; footsteps of the divine is only Cleric 3rd.)
