Conclusion
Looking up the price for 8GB kits of F3-2666C11D-8GTXD, we see offers currently starting at 123 Euros excluding shipping across the EU. The only offers that could potentially beat the Trident-X are a cheaper DDR3-2600 set from Adata and a much cheaper DDR3-2666 set from Team Group. While this pair of kits might be able to show better ratios of stable timings, voltage and frequency, Hynix MFR chips that they are likely to use are not going to bring any performance benefits due to single-sided configuration of the modules.
In the end, we can say that Ivy Bridge-born memory models are still a force in the Haswell era, as clearly demonstrated above by the DDR3-2666 CL11 version of the Trident-X. Not only are Hynix CFR memory chips, which this kit is still based on, able to show good overclocking numbers, but those are also likely to outlast (in terms of production runs) and outperform any of the alternatives currently available. And they achieve all that while being reasonably priced, which deservedly gets our thumbs up.
Award
The 2x4GB version of G.Skill Trident-X DDR3-2666 gets an ocaholic rating of
4.5 stars out of five.
Kingston HyperX 10th Anniversary 2x4GB DDR3-1866 CL9 1.65V Review 