Beverly Cleary's Henry Huggins books are high-4th / low 5th, have a boy protagonist, and are well-liked by my 7yo.
We've got a similar problem - her beginning-of-year STAR test gave her a grade equivalent of 6.3 (which IMHO vastly overestimates her reading level - I'd put her at about mid-5th now, which is ~10 weeks later). We have a hard time finding 4th grade books (the level she's "earned" at school - she has the ability to move up to 5th if she were interested in jumping through the appropriate hoops) that are the right interest level for her. For a long time, books with too many pages or too-small of type were too intimidating. And now she's reading longer books, many don't work out because the subject matter isn't interesting. (The Percy Jackson books dealt with "too old" material, for instance.)
