S4 Neck: http://www.wowhead.com/?item=35135
39 Stam, 26 Crit Rating (1.18% Crit), 18 Resil, 58 AP, and a socket.
Shattered Sun Neck: http://www.wowhead.com/?item=34679
18 Agi (.72% Crit, 1.22% Dodge), 19 Stam, 64 AP. The Aldor proc is +200 AP for 10 seconds, and the Scryer is 333 to 367 damage Arcane Strike.
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The SSO neck has 24 more AP, .46% less crit, 1.22% more dodge, 20 less stam, and you lose 18 resil.
If you ask me, I'd probably still roll with the S4 neck because of the loss of stam, resil, and crit. The 24 less AP without a socket is small, and can be gained elsewhere, through gem changes or enchant changes. If you were going to use a PvE item, or neck rather, the only ones that would be worth losing the stats over are probably in deep BT or Sunwell. You're better off replacing your Veteran's (or in S4, Vindicator) ring for something with much better DPS stats.
If you go to one of the previous topics (https://chrille.forumotion.com/feral-f3/staff-of-the-forest-lord-s3-staff-what-do-u-think-t25.htm) I gave an idea of what ring to go for, and the stat differences.