You should have hesitated longer. Most of these issues have been discussed, except for the ones specific to your character (which we don't care about). Search and read before posting.
I almost hesitate to post this, but improving my personal dps comes before my pride. So:
I had taken a bit of a break waiting for 3.1, previously playing my mage mostly and raiding on my DK as 0-33-38 dual-wield spec. Since my return to the game, I decided to adopt blood as my new spec.
For the point of reference, my armory is The World of Warcraft Armory
(Also I've noticed that it doesn't factor talents into that anymore. Not quite sure why, but with horn I'm sitting at 4k AP, 32% crit, 8% ArPen, 11% haste, 269 hit, and 27 expertise.)
Now, I know my trinkets (At least one of them) definitely needs an upgrade. Frustratingly, I never saw Grim Toll drop. Now there are of course more options out of Ulduar as well, as well as a Greatness Card (Fun times being too broke for it. Slowly acquiring the deck though). Aside from that and my heroes shoulders and belt, everything else is ilvl 213 or 219. I have my 4p with the Valorous chest, as well as my Undimished Breastplate. I haven't had any issues with generating runic power, so I'm currently wearing the Undimished for the hit and to cover dodges with expertise.
I'm using glyphs of DRW, DS, and Disease.
My rotation is, as best as I can keep to it:
PS > IT > HS > HS > DS > DC > DC
Pest > HS > HS > HS > HS > HS > DC > DC
Pest > HS > DS > DS > DC > DC
From my last raid, on thursday night, we started our attempts on Mimiron. After 20 attempts we did get the kill, but my average dps through them was about 3.6k and my best attempt was 3.9k.
3.6 - 3.9k dps seems extraordinarily low, especially compared to everyone else in my guild. I'm convinced that with my gear level I should be able to do far more. I abhor the idea of being carried, and I really feel like I was that night. Especially since I could do 5k+ with my old spec (With generally worse gear).
Which brings me to my questions...
I'm using a glyphed pestilence to refresh my diseases, for several reasons. First, it keeps their timers equal. Second, It frees up the use of 1 GCD and 2 runes. It leaves me with an extra frost and unholy rune, thus another DS instead of PS/IT. Or, if I have Death Runes up, I get 5 Heart Strikes out of my set of runes.
Despite my assumptions here, pestilence does zero damage whereas PS and IT do.
Are my ideas in fact correct, or would it be better to use 2 runes/gcds to refresh diseases with PS/IT? Is using a GCD that does no damage in fact going to gimp me despite the extra DS I get from it?
In regards to 4p t7 set bonus. As I said earlier, I really have had no issues running out of RP without it. With it, I simply have so much I don't even know what to do with it all. Really, it seems more beneficial to have that extra 100 hit (because I'm morbidly low without it) and the expertise puts me past the 26 for dodge cap. Without it though, I still don't typically have too many more misses/dodges. It's been in the single digits every time, though my glancing blows on white damage is a good 10% higher on average I'd say.
Is having that extra hit worth breaking the 4p for? I've read so much about how great it is, but I've failed to see the practicality in faster runic power over fewer missed strikes/hits. Looking at it from the other point of view, DS hits significantly harder with more RP.
I do enjoy playing as blood, but it's a style of play unlike anything I've ever done. My DW spec was very caster-oriented with IT/HB. This is the total opposite and definitely feels foreign to me still. So I'd really appreciate any insight into all this, or any suggestions on improving my overall dps.
Edit: i've been up all night, apologies for any incoherent sentences. I tried not to ramble but my mind is pretty dead right now.