You assumed that if you want to go 2/2 demonic power you should take these points from Nemesis which is just wrong.
http://armory.warmane.com/character/...ecrown/talents
What you don't need is 2/2 intensity for pushback occurs in few encounters like marrowgar or rotface which are easy and short fights anyways so there's a waste of 1 important point which could give your imp huge dps boost (see screenshots below). Of course pushback happens in situations like when you aggro ghouls on LK or adds @ Lady but for what it's worth the most interesting encounters in ICC do not require of you to have 2/2 intensity (in worst case scenario its like +0,1 - 0,2 sec in your casts).
And then you can put these points for your imp. I'm not going to argue about your calculations of the immolation aura on LK and valkyrs its more dependant of your gameplay when you use your cooldowns on valkyrs - meta, immolation aura target your valkyr/spam seed of corru but again you assumed that I loose some points from Nemesis which would mean my meta has longer cd.
My meta cd is exactly 2:06 so it combines pretty good with racial + engi speed I can use meta twice on almost all fights except maybe Marrowgar and some lazy encounters like Blood council (who cares :D).
And lastly I've checked your imp damage and compared it to mine, it's not 400 dps difference but more like 1k which is a lot.
http://imgur.com/a/QtV6v
The one without name of the boss is actually Prof hc, your Festergut with BL and mine without is still a difference of ~~ 600 dps and @ DB hc mine does almost 1,2k more.
There's a date on my screenshots in the right lower corner so you can see when I have made them. This soulfire was not buffed in any way like tots ( I wish :D ) just flamecap and meta.
It's difficult to compare dps when we are playing in different raid conditions, I would like for instance to do one raid (or two) with much higher average dps just to test myself.