hey man, this thread will get locked - use this thread for DPS related issues:
http://www.mmo-champion.com/threads/...-My-DK-DPS-MoP
a quick look at your armory shows you at 10% hit... swap your blue gems for str/stam and take hit off your cloak (replace with crit)... Then enchant your bracers :-D
Spark is not holding you back, it's not AS good for festerblight but you won't be using festerblight for every fight this tier anyway (in a realistic scenario) and spark is actually better for fights like jin'rokh as the proc lines up with the first pool.
If you're comfortable with a specific spec then that's the one for you, whether or not Unholy should do more damage is irrelevant if you're not good at playing unholy in the first place.
Most of your logs seem to be frost and, even if I found an unholy one (to compare it to mine) I raid 10man so the damage done would likely be different. There are a number of threads regarding festerblight, unholy, talents, frost and whatnot on the forums and elitist jerks etc - if you've exhausted all those avenues then all I can say is "practise" or "stick with frost"
EDIT - A friend of mine likely won't mind me using his logs ;-)
http://www.wow-heroes.com/character/eu/Draenor/saybel/
^^ have a look through and compare