imp does around 450-600dps depending on encounter and makes up 6-9% of my total damage as full destruction (0/13/58)
back when i last played a demo spec (0/41/30) my felguard pushed out 18-25% of my damage depending on fight (usually 19-20% but there are a few fights it does alot more % ways 'cos you have to move alot) so around 1000-1200 dps back when i played it.