Default settings are almost always JEDEC standard settings, and those are 2,6V max. for 400MHz JEDEC profile kit (and 2,5V for every other profile).
2,8V is what OCZ wants you to set to get 100% stable at timings and frequency described on package/stickers. RAM obviously can work on multiple different profiles set in SPD.
Check CPU-z "SPD" tab for more details about settings available to your RAM modules.
@up "RAM for overclockers" is a guarantee OC up to set point, specified by manufacturer (warranty covers any stability problems if said RAM can't work on it).
Normally you don't get that and have to resort to serial or revision checking to get best quality RAM.
Of course you can "cherry pick" Overclocker's RAM as well 😉
PS. I personally don't like those high profile RAM kits (OCZ heatpipe DDR2 is overkill).
They are bulky, and in most MB's can't be put besides each other without bending memory slots (require mix-matching for 4 module configuration).
There's also that CPU heatsink height/width problem (too small, and RAM/cooler can't be mounted).
I prefer to search for best IC's "under the hood" and pick ones with standard size heatspreader.