Thank you for the detailed answer.

In an odd way, I am glad the landscape is so complex and unpredictable

I was wondering for pvp Sub rogue am i losing more dmg output by switching to Maces/Swords/Axes then if i go daggers? Also i dont use backstab too much seeing as it is harder now to keep enemy down in pvp with all the kiting. Any feedback be great because everyone i ask i get 50/50 answers some people say i wont do as much damage with other weapons as daggers some say it doesnt matter..

You can use PowerAuras to have a sign flash when the boss hits 35%. I suggest you also have it accompanied by a loud sound so you don't have to watch the bars at all. All in all, a very convenient addon for a wide range of situations.

You can also turn on that option in Deadly Boss Mods. Pretty much every raiding guild required DBM, so you already have it built in. It's somewhere in the options, and it will show up as a bar with a percentage of health on it.

Target Percent is about as simple as it can get

I use Power Auras for this. You can set it to show an icon when your target's health is at and below 35% and you can make it flash and do all kinds of "attention grabbing" type things. Very Helpful.

Thank you, this is what I was looking for.

If you download powerauras just import:

Set=Page 1@ Aura[1]=Version:4.4; icon:Ability
_Rogue_Disembowel; buffname:Envenom; x:-75; g
roupany:false; alpha:1; owntex:true; isRestin
g:0; mine:true; spec2:false; size:0.21; y:-20
5; texmode:2; ismounted:0; timer.h:1.18; time
r.enabled:true; timer.y:-165; timer.x:-83; ti
mer.Transparent:true@ Aura[2]=Version:4.4; ta
rget:true; icon:Ability_Rogue_Garrote; buffna
me:Garrote; x:73; groupany:false; bufftype:2;
alpha:1; owntex:true; isResting:0; mine:true
; tooltipCheck:every; spec2:false; size:0.21;
y:-278; texmode:2; ismounted:0; timer.h:1.18
; timer.enabled:true; timer.y:-242; timer.x:6
3; timer.Transparent:true@ Aura[3]=Version:4.
4; icon:Ability_Hunter_RapidKilling; buffname
:Overkill; x:-136; groupany:false; alpha:1; o
wntex:true; isResting:0; mine:true; spec2:fal
se; size:0.21; y:-155; texmode:2; ismounted:0
; timer.h:1.18; timer.enabled:true; timer.y:-
118; timer.x:-147; timer.Transparent:true@ Au
ra[4]=Version:4.4; target:true; icon:ability_
rogue_deadliness; buffname:Vendetta; x:136; g
roupany:false; bufftype:2; alpha:1; owntex:tr
ue; isResting:0; mine:true; spec2:false; size
:0.21; y:-155; texmode:2; ismounted:0; timer.
h:1.18; timer.enabled:true; timer.y:-118; tim
er.x:126; timer.Transparent:true@ Aura[5]=Ver
sion:4.4; icon:ability_rogue_recuperate; buff
name:Recuperate; x:-75; groupany:false; alpha
:1; owntex:true; isResting:0; mine:true; spec
2:false; size:0.21; y:-278; texmode:2; ismoun
ted:0; timer.h:1.18; timer.enabled:true; time
r.y:-242; timer.x:-83; timer.Transparent:true
@ Aura[6]=Version:4.4; anim1:4; target:true;
icon:Spell_fire_meteorstorm; x:-259; bufftype
:8; texture:10; alpha:0.5; threshold:35; spec
2:false; size:2; y:269; texmode:2; ismounted:
0@ Aura[7]=Version:4.4; icon:Ability_Rogue_Sl
iceDice; buffname:Slice and Dice; groupany:fa
lse; alpha:1; owntex:true; isResting:0; mine:
true; spec2:false; size:0.31; y:-213; texmode
:2; ismounted:0; timer.h:1.5; timer.enabled:t
rue; timer.y:-159; timer.x:-13; timer.Transpa
rent:true@ Aura[8]=Version:4.4; target:true;
icon:Ability_Rogue_Rupture; buffname:Rupture;
x:73; groupany:false; bufftype:2; alpha:1; o
wntex:true; isResting:0; mine:true; spec2:fal
se; size:0.21; y:-205; texmode:2; ismounted:0
; timer.h:1.18; timer.enabled:true; timer.y:-
165; timer.x:63; timer.Transparent:true@

That sets up an animation to happen when your target is below 35%. I've never used it personally, I did it manually.

Here's my source: Setting up Power Auras to remind you to backstab « Forever a Noob – A WoW Rogue Blog

Looking ahead a few weeks, which is the best non-set piece to go for?
At first glance it's either Sark of the Unwatched or Poison Protocol Pauldrons, although there's also the Haste/Mastery legs from Al'Akir to consider.

So which would be the most optimal setup to go for?

I'm not sure for Mutilate but looking at the stats for Combat, the tier leggings seem to have the weakest stat allocation. There are nice leggings off of Maloriak that could replace these as our offset piece.

Actually they're not, since there's no other profession for Melee and you have to give up a profession for it.

When comparing another 80agi profession (Or Leatherworking)+tier helm vs Agile Bio-Optic, then the Engineering helm looks less than appealing.