The M119A2 has a 19.2Km range with RAP. The Denel G7 has a 40Km range with a VLAP projectile.

The 105 has a drawback in effects, because the 120 has a lot more effect on the target than a standard 105, and the RAP round has even less explosive.

Fundamentally you have to make a choice between range and effect. The angle of fall on a mortar has some advantages, too.

The 155 just has a longer range and slightly better projectile design. The cost is size and weight.