I run the cheapest 87 I can find, and it works just fine. I get 26 mpg around town and almost 30 mpg on drives to the City (all freeway, 100 miles each way). There is no good reason to use more octane than you need, it just lightens your wallet.
The only caveat is, it is prudent to run an injector cleaner like Chevron Pro-Gard or Clean-Up, Red Line SI-1, or BG44K every 5 - 10k miles. I typically use Chevron, but have used both the Red Line and the BG products. BG is the most expensive at about $16 per dose. Chevron and Red Line are about $7 a dose and are widely available.
The only caveat is, it is prudent to run an injector cleaner like Chevron Pro-Gard or Clean-Up, Red Line SI-1, or BG44K every 5 - 10k miles. I typically use Chevron, but have used both the Red Line and the BG products. BG is the most expensive at about $16 per dose. Chevron and Red Line are about $7 a dose and are widely available.