After more investigation, including trying single sticks at a time in every mainboard slot, I determined that the RAM is indeed quite finicky for overclocking. For example, at one point the machine would not boot with the memory at around 1100MHz with quite loose, manually set timings, however when timings were set to SPD Auto, the machine booted smoothly with lower timings than I had previously attempted. All in all, though auto settings often returned timings lower than those listed in the SPD, the general flexibility of the modules was very low.
Though the Aeneon XTUNE kit runs at the lower frequency of 1333MHz, this far in the DDR3 game, most modules run at the same speed. One of the major differences about the XTUNE kit, though, is that it runs at 1.5V. On the whole, many companies have yet to wean off of the voltage addiction brought on by heavy overclocking on DDR2, so the 1.5V kits always seem to take hits not only in performance, but in price as well. Through my experiences with the XTUNE kit, however, any clock it could reach could be reached at the stock voltage of 1.5V; for the most part, adding to the VDIMM had no helpful effect. This goes to show that Aeneon successfully designed their kit to run accurately and solidly at the low 1.5V.
Aeneon certainly hit the market early with their XTUNE kit, and it shows with the memory's overclocking ability (or lack-there-of). The sticks simply do not run very well at any custom settings, and adding voltage was no help either. It's a bit confounding that neither adding voltage nor loosening timing helped with frequency overclocking and it's disappointing that the end user can't take advantage of the low stock voltage and really pump these sticks above and beyond.
All DDR3 memory is very expensive, and so is the Aeneon XTUNE kit, but related to its competition it is very fairly priced. Though this RAM is geared at the overclocker, I would more readily recommend this kit to the user willing to keep their memory at stock speeds.
Special thanks to Aeneon for providing us with this review sample.