How to Play fast Melodic Death Metal Riffs?

Hey everyone, I am an Intermediate guitarist, i know the following:

Hammer on Pull off
Slides
Basic Fast Legato (Not too Fast Though But Fast)
Palm Muting
Really Basic Tremolo Picking (alternate Picking) (Max Speed is (On
120bpm) Sixteenth Notes)
Upto Whole Step Bends (And on Higher Frets Even One And a Half)
Behind The Nut Bends
Power Chords
Basic Chords

And Yeah But I have Always wanted to play Melodic Death Metal
Basically I mean Rifsf that Have Normal Melodic Stuff But With Really
Fast Open Strings In Between if you Cant understand what Im Talking
About, Listen to The intro of 'Deadly Sinners' by '3 Inches of Blood'
Or 'They Will Return' By 'Kalmah' I relly Love those Riffs. Basically
I can Do Fast Picking But Cant do fast Picking On Two Strings One By
One, I mean I cant Do this (Just an Example):

E-0-0---2---0---7---3---5---0---7---2---3---5---2-0-3-5-3-2-0
B-------0---0---0---0---0---0---0---0---0---0---0------------------

(Meant To be Played On Sixteenth Note At 120bpm)

So Please Guide Me To develop Speed Or Any Sort Of tip Will Help.