According to the stats on the Brink wiki, the Maximus LMG is basically a Gerund with a larger clip. They supposedly have the same per-bullet damage and ROF. However, my kills/hour with the Maximus are significantly higher than with any other gun I’ve used, and it really seems like the Maximus is doing much more damage than an assault rifle.
Some of the difference is clip size and increasing game skill, but not all of it. Is there some other hidden stat for heavy weapons? Is the wiki mistaken?