Are there any 40MM fans designed for 7.2V?

If I had my druthers I'd get a fan that was designed for 7.2V, since anything under or over the rated voltage reduces fan efficiency, assuming they are designed properly.

That's a near-worthless factor within the RC tank world (I understand my certain OCD tendencies lol), but IF one were available as reasonably as all the other fans out there, that's what I'd opt for.