Both the initiation and upkeep of the spells are affected by LMC.
Tribulation
At 40 LMC this would drop it to 18/10 from 30/16
With 0 Mana Regen/ Second at 100 mana it would give 8 rounds before expiring. (16 Seconds)
Despair:
Would be 18/11
At 100 Mana with no Mana regen this amounts to 7 Rounds of damage before expiring. (14 Seconds)
(At Max skill this is 448 Physical damage After reducing the target's strength by 32.)
At 0 LMC with 100 mana, it would be 3 Rounds, (6 Seconds) and 192 Physical Damage + the 32 Strength Reduction (Its actually 3.88 but for the sake of argument lets ignore any round fractions)
At 40 LMC The equivalent in magery for damage would be approximately 5 Flame strikes and 1 Magic arrow that mana cost would be about 126. And the cast time would be ~12 seconds.
At 0 LMC The Equivalent for magery would be 2 Flame strikes and maybe a punch

.
The mana cost for the Mage would be 80, and the cast time would be 4 seconds.
The longer the bard song is in effect, the total cost for value is lowered. While in the case of the mage, its a constant linear growth.