finding supportable a sentencing court's drug quantity determination when it was based on witness testimony

concluding the trial judge's careful and thoughtful consideration of a jury's potential bias revealed through a note sent to the judge during trial resulted in a "reasonable and appropriately measured" response

explaining that "defendants' five-year wait for trial" was gravely concerning but nevertheless did not violate the Sixth Amendment where it was counterbalanced by defendants' "contributions to the pretrial delays" and failure to show "how their ability to mount an adequate defense was hampered by the delay"

explaining this court's concern with the government's practice of "monolithically process[ing] ‘mega-cases’ " that result in some defendants -- presumed innocent -- waiting incarcerated for years while the trial court resolves codefendants' pleas and motions