upholding as reasonable a sentence longer than that imposed on codefendant, even though codefendant’s Guidelines range was higher, where that codefendant had cooperated with the government | upholding as reasonable a sentence longer than that imposed on co-defendant, even though co-defendant’s Sentencing Guidelines range was higher, where that co-defendant had cooperated with the government | upholding as reasonable a sentence longer than that imposed on a co-defendant who cooperated, and noting that a "sentencing difference is not a forbidden 'disparity' if it is justified by legitimate considerations, such as rewards for cooperation” | “[tjhe determination of sovereignty over an area, the Supreme Court has held, is for the legislative and executive departments” | “We repeat that the presumption before us is an appellate court presumption.”