Vanderbilt admits a significant percentage of its freshman class via ED, and consequently the school’s preference for very high test scores is even more pronounced in the RD round. My daughter, for example, applied RD to Vandy and was wait-listed with a 2300 SAT and a 3.98uw GPA. At WashU, by contrast, she was accepted RD . . . and offered a merit scholarship to boot.
I would think, however, that with a 2400 SAT and a 3.9 (and appropriate essays and recommendations), the OP could feel pretty confident of admission to Vanderbilt in the RD round, thus saving the EA/ED option for an even higher reach.