Varying your anchor text is an accustomed SEO practice. It's not unethical at all. I change my anchor text from time to time to get ranking for various keywords. If you can hit two birds by one stone, why not!?
Damn, this is probably the reason why i got bumped down a page in rankings on my rocket french review site. I created many article links but they all have the same anchor text. Learnt something new! Thanks