I beat all the Hammerhead missions on Insane, never had that much trouble with them. The trick is to play cheap and just shoot them from outside their firing range
or if you get close just keep constantly moving back and forth/up and down, makes it so that you can avoid pretty much every slow firing weapon.
As for loyalty speech options, I never had any paragon options greyed out during my 1st playthrough. Then in my NG+ I've had them greyed out several times - Jack/Miranda's fight, fighting Morinth's mind-control thinger, convincing Zaeed to not be a dick. And considering both playthroughs are paragon....I dunno. Apparently it's not only your paragon/renegade points that matter, but how many paragon/renegade decisions you've made and what level you are at the time (the higher level you are the more points you require to make a paragon/renegade action).
Not sure how much of that is true, there's a lot of conflicting info out there.