1) Those who continue to call for an FBI investigation are either a) uninformed or b) partisans. Remember, the goal of this particular exercise is to inform Senators of facts (it isn't a criminal inquiry) An FBI investigation is black hole, in which Senators have no role/control
2) A Senate committee investigation can be every bit as thorough--as evidenced by the many people that have been contacted already. But here is the big difference: Senators can demand who gets contacted, what questions be asked, see immediate answers, demand follow on.
3) If your only interest is delaying a nomination, yes, you'd call for an FBI investigation--since it would take a long time and keep everyone in the dark. But if the goal is informing senators before a vote, the committee is absolutely best vehicle for the job.
