I know a Guard player who takes Vendettas (which can fly directly into your spawn and fire 6 Lascannons each at your units), Artillery (which do not require line of site) and scion command squads (incredibly cheap plasma spam). He could whipe you in a turn if he stole the initiative, though his list is extremely competitive. Also, he runs a 50 man conscript unit which lines up on the edge of his spawn, spaced out to prevent deep striking anywhere near his tanks. If you come across a Guard player like that you'll not be very happy (neither was I

). As I said though, the Changeling's aura can help prevent that kind of alpha strike.
The calculation is including supercharging.
I'm not much a fan of summoning since too much is left to chance. Though if I was going to summon something I would summon Bloodletters or Seekers since it would be a good way to get them into combat. I suggest to you however to summon as many units of 1 Blue Horror + 9 Brimstones and drown your opponant in smite.