I win roughly 80% of my matches with dual IG-88 and I play them at least once a week and against some dangerous lists, like Redline/Whisper/other. Most of my victories end up with scores such as 200-50 or 200-100, but I've hit several 200-0 and a few 200-150 (rare).
As others have pointed out, IG-88 does not shine in terms of action economy, so I suggest not even trying to. Those killer robots do not have action economy, but with advanced sensors on IG-88B and IG-88A, they have action "consistency". Once you get past the initial alpha strike (and learning how to deal with that part is where the trick lies), if you managed to wether the storm, those little buggers will get behind an opponent and be a royal pain.
Got to find the right strategy though, which is not always easy.