Keep in mind that reading levels can be a bit misleading. DRA', AR are often based on the vocabulary, syntax and overall complexity of the writing - rather than the themes and ideas.
For many gifted kids, it's the themes and abstract concepts that challenge and interest them - more than the level of decoding that the book requires. Books like those from the Harry Potter series can be be very rich, if one delves into some of the overarching social themes - even if they are relatively easy in terms of vocabulary and sentence structure.
Try going onto your and neighboring school district's websites to find out what is being assigned for Middle School. These books are often screened for sex and violence (to some degree) but offer rich story lines and abstract ideas. Here are some that my kids have enjoyed:
Life of Pi
Water for Elephants (one highly sexual scene - we listened to the audio and I ff'd through it)
To Kill a Mockingbird
Nation
A Walk in the Woods
A Prayer for Owen Meany
Ishmael
Esperanza Rising
My Side of the Mountain
Tuesday's with Morrie
The Curious Incident of the Dog in the Nighttime
Whale Talk
My Sister's Keeper
