Rampage x1 is rarely useful on its own, even with additional outside damage buffs like Radiant or a high Weapon stat. You generally need x2 or maybe even x3 before it starts really affecting your TTK. Kill Clip, on the other hand, is frequently enough by itself to lower TTK by a bullet for most weapons. If that's your concern, go with Kill Clip, even though it needs a reload, since even in the case of being forced to immediately change to a new target without reloading Rampage x1 likely wouldn't help in that fight either anyway. Rampage is basically the worst of the "non-reload" damage buffs and I wouldn't ever seriously consider using it. The game has become much too fast and ability-focused for it.

If the numbers I'm looking at are right, neither change the bursts to kill by themselves But a combination of Kill Clip, Surge mods, and a high weapon stat looks like it make a 2 burst possible I think