Your Link Request Email is Unsolicited Criticism
In many cases your cold link request email is an unsolicited criticism of your link prospect's website.
It's unsolicited because your link prospects didn't seek you out and ask you how to improve the value of a page on their websites.
It's a critique because you imply that your link prospects' omission of your link forces their site visitors into a substandard experience.
If your site happens to be old and well established you imply that their visitors may notice their omission and think less of his knowledge of the space.
If your site is new or unknown you imply that they are missing the opportunity to grow their reputation as a well informed curator of his space.
No matter how you position your request, it's still an unsolicited critique that requires action.
You must demonstrate why you're qualified to make unsolicited criticisms of your link prospect's website.
The quality of content at your URL should do most of the qualifying. Further, where in your space have you been published? Who else has linked to this particular URL? What have others in your space said about this URL?
Conveying this type of information qualifies your unsolicited critique and will increase your link request conversions.