EmEditor should handle this. As their site claims:
EmEditor is now able to open even larger than 248 GB (or 2.1 billion lines) by opening a portion of the file with the new custom bar - Large File Controller. The Large File Controller allows you to specify the beginning point, end point, and range of the file to be opened. It also allows you to stop the opening of the file and monitor the real size of the file and the size of the temporary disk available.
Not free though..