Both companies are correct. Essentially Intel will void your warranty if you go above 1.5v (if you tell them). 1.6v is almost certainly required to get you up to 2133. A quagmire.
What we're talking about here is OverClocking. If you're not familiar with this, run the RAM at 1.5 and 1600/1333 until you've had time to read up on the topic. A good place to start is in the Overclocking section of Toms Forums:http://www.tomshardware.co.uk/forum/forum-11.html
Bumping just to 1.6v isn't a big jump, and there are tons of people out there that do it successfully. You just need to know what you're getting into... I can't just blindly tell you "it's OK to do it".