Those Diabolic Revelation s don't seem to be looking all that useful, it's got a high mana cost which is something you need for extortion. Try adding more creatures with deathtouch and lifelink, maybe Tithe Drinker or Child of Night .

I use Diabolic Revelation to get more Crypt Ghast 5th turn, so 6th turn I can mana ramp big time with Debt to the Deathless

You could try Liliana of the Dark Realms dig for swamps with her +1, then use her ultimate to make all your swamps tap for 4

Im not really having a problem with mana. Im having a problem with speed.

:|

Doesn't more mana mean more speed? The more mana you have, the more you can pay for X, meaning the more damage dealt, meaning they get closer to 0 life faster. Mana = speed.

I don't see how else you could speed it up. A turn 6 win is pretty nice, it just sounds like you need to slow your opponent down. Perhaps more removal like Oblivion Ring and some of Azorius' mono-white detain, like Lyev Decree would allow you to get to turn 6.

in with Unforgiven. your problem isnt speeding up the deck your problem is you need to slow THEM down. you need to do 2 things. maximise teh comob your trying and take out EVERYTHING that isnt vita to it. then you need to fill the spaces with control like O-Rings. Tragic Slips. etc. also this deck is really cheap and so dont be suprised when your getting creamed by 500 dollar net decks

Why Lyev Decree ? It seems like some hard removal like Orzhov Charm would work better. Especially with the lifegain the downside on Orzhov Charm isn't an issue, and you get a little bit of flexibility.

I'd also up the Exquisite Blood , since with the guildmage it gives you that infinite loop. Maybe take out some Diabolic Revelation , it seems expensive and I'm not sure how often you'll need it (you'll know better though with playtesting).

Sign in Blood might be better card advantage as it will give you something to cast on the early turns while you're waiting for your big spells to become playable.

I agree with potatoedoughnut. An Orzhov Charm would be your best bet because it allows for low mana cost removal without it really doing that much damage to you since you can rake up health. Also it can be used to keep your Vizkopa Guildmage if someone targets it with a removal spell.