One thing to remember about impact though, it appears to be relative to other guns of that class so you can't compare the impact of, say, a scout to a sniper. The best scouts have 80% full impact bars, while the best sniper is only like 40% full. A sniper will still do way more damage per shot, unless the scout is much higher level/attack rating. Likewise, a high-impact fusion rifle will have 95% of the bar, but I still don't think it does more damage than a sniper even if all the shots land as precision strikes. Maybe it's a little bit more, but it's certainly not more than double.
Not sure why they made weapon stats so needlessly obtuse. This shit should all be written in plain text/hard numbers instead of vague bars with no scale marked on them.