I do not plan to overclock much, for me system stability and longevity is paramount (I never turn off my PC)
1. Which one of the above should I use (I stream PS3 media server from PC, and do some WoW and Battlefield 3, but mainly Office and Photoshop)
2. Is installing quad-channel memory on two-channel mobo is simply a waste of money?
3. Would you rather suggest to drop to two-channel memory altogether?
4. Which memory would you then recommend for the best performance, and utilizing of TurboBoost for i7 processor, and maybe some minimal overclocking?
On the LGA 1155 platform there's only a tiny improvement with DDR3-1600 CAS 8/9 over the rest. Further, ultra low CAS + higher Frequency is often less stable. Next, though not listed above, placing together (2) Kits frequently doesn't yield the indiviual Rated per set.
A 4x4GB kit is fine, but anything >DDR3-1866 is IMO a pain to keep stable and error free.
CMT16GX3M4X2133C9 - is primarily an LGA 1156 kit, but will work though risking BSOD/errors
CMP16GX3M4X1866C9 - is primarily an LGA 1156 kit, but will work
CMP16GX3M4X1600C7 - is primarily an LGA 1156 kit, but will work
IMO for Corsair:
Also, the newer 1.35v kits are good; I just received CMZ16GX3M4X1600C9G and they're fine.
Is there a principal difference between the Dominator and Vengeance?
Is Dominator designed for 3-channel mobos, and Vengeance for 2-chennel?
Would there be a performance penalty if I install Dominator on Z68 1155 2-channel motherboard?
The price on Newegg for 1866 16 GB modules is the same, but the fact that Dominator is hand-picked and tested all 4 modules to work together, appeals to me. If there are no performance penalties stemming from 2 vs. 3-channel design, I think I would opt for Dominator.
Or would you advise to go for Vengeance, if so, why?
The differences are subtle and the CMT is a revamped LGA 1156/1366 kit; as stated they'll work. Just don't use 1.65v RAM on the Sandy Bridge; granted most kits >DDR3-1866 are going to be 1.60v~1.65v.
The Dominator and Vengeance use slightly different IC's, they both can come in Dual, Tri and Quad Channel kits. The newer Vengeance are the lower voltage kits for the most part. Dominator leans towards higher voltage. It all depends upon what specific kit of either, I'm giving you an overview.
The 'Why' is explained above, and I assume you read the Article I linked above. The Vengeance is designed for the Sandy Bridge with 1.50v and lower offerings e.g. 1.35v.
The Dominator (CMP/CMT) primary comeback is primarily geared towards the LGA 2011/X79 + SB-E. The IC's used offer better latitude (performance) where a BCLK increases can be set. In contrast e.g. the LGA 1155/Z68 has nearly no room for a BCLK OC (98MHz~107MHz), and in contrast the LGA 2011/X79 can be set from 100MHz to 133MHz+, dual clocks, can again handle the 1.50v~1.65v DIMM, and actually do benefit from DDR3-1866~DDR3-2400 RAM. This is similar to the LGA 1366/X58 days of BCLK OC when the Dominator was the idea choice - hence it's comeback.
So it's not a question of 'working' it's more an answer to the best LGA 1155/Z68 environment, it's limits, and ideal/known good choices.