How to gain 140m exp in 4 hours

140m*1.3=182m

You just missed 42m by not equipping the pendent, can 10atk help you gain this much exp?

The MoN helps reduce the kills needed of Oblivion Guardians by one hit. To make it more equal we have to cut down the EXP by about 15-20%.

140m * 0.85 = 119m
119m * 1.3 = 154.7m

140m * 0.80 = 112m
112m * 1.3 = 145.6m

Oh wow, equip the Spirit Pendant for a mere ~5-14m extra EXP at the cost of burning more pots?

No. Just no. That's with a full 130% bonus as well. Imagine with a weak 10%/20% two hours. EXP/hour would roughly equal out, or even goes down WITHOUT a MoN.