ok so I figure I might as well do a fallow up on this post.

I went with a nec/ranger

mods to bows might really help. I'll test later wen I can find them.
put as many points into death as possible for making summons last long to prevent recasting.

Gargoyle Skulls = summoner and bonus bow/gargoyle. Let me know if any one knows of elemental weakness's.
Unnatural Seeds = all builds are the same. summoner is not faster due to it clears all enemies.
Baked Husks = summoner and low q bow/Worm. Let me know if any one knows of elemental weakness's
Skeletal Limbs = I just saw the skullreaver video and it seams to be the best.. so ya use symbol of wrath
Dull Carapaces = death skill's and cold/low q bow/Devourer. (Wiki say) weak to fire and cold dmg. Ascalon have -20 arm vrs cold dmg. I have not confirmed.
Grawl Necklaces = death skill's and cold/max dmg gg inherit bow/grawl. (Wiki say) weak to lightning(might only be shiverpeaks) and cold dmg. I have tested this and thay defiantly are weaker to cold. I have not tested the VQ grawl.

A person might want to make gg bows for VQ. I have not tested this build against VQ's yet.
I have not found or know of humans, charr's, skely's and zombie(undead) having any weakness's. Let me know if any one knows of elemental weakness's.
ps. undead are weaker to holy damage.

NOTE: this build might be pointless due to I cant find much info on loot scaling and diminishing returns. pleas fill free to comment.

EDIT/Up date: Ok Soo...
There is no Of Species(slaying) =+18% vs Species for these listed above   . So I'm left with testing ;

dull car BOW. 20%(persiniliz) + 14%(Over 50% hp or While Enchanted) + prefex(Icy) + 18% marks
.

grawl BOW... 20%(persiniliz) + 14%(Over 50% hp or While Enchanted) + prefex(Icy) + 18% marks. I bet a max dmg bow and mods will not kill in 1 hit. I have to play with cold dmg                         I TESTED bonus bow and char at 9 marks attribute. Does not kill grawl longspear in one hit
. 

worm Bow.. 20%(persiniliz) + 14%(Over 50% hp or While Enchanted) + prefex(Sundering +18% arm pen) + 18% marks.


Gargoyle BOW. 20%(persiniliz) + 14%(Over 50% hp or While Enchanted) + prefex(Sundering +18% arm pen) + 18% marks.  I bet a max dmg bow and mods will not kill in 1 hit

EDIT: ok up date;
dull car BOW. 20%(persiniliz) + 14%(Over 50% hp or While Enchanted) + prefx(Icy) + 18% marks. plane max dmg bow might kill

grawl BOW... 20%(persiniliz) + 14%(Over 50% hp or While Enchanted) + prefx(Icy) + 18% marks. bonus bow + 10 marks might kill with marks mod

Gargoyle BOW. 20%(persiniliz) + 14%(Over 50% hp or While Enchanted) + prefx(Sundering +18% arm pen) + 18% marks. bonus bow + 9/10 kills. Max dmg bow might kil

worm Bow.. 20%(persiniliz) + 14%(Over 50% hp or While Enchanted) + prefx(Sundering +18% arm pen) + 18% marks. plane max dmg bow might kill

I tested cold resistanc on the grawl by using cold sworm
                bass dmg/dmg vs grawl
lvl 0 cold swarm 30/38 dmg vs grawl(normal 80hp) 34 vs grawl(longspear)

lvl 2 cold swarm 38/48 dmg vs grawl(normal 80hp)

lvl 6 cold swarm 54/68 dmg vs grawl(normal 80hp)

lvl 12 cold swarm 78/98 dmg vs grawl(normal 80hp) 88 vs Grawl(longspear)

What about Power Shot mrkvagusara?