I don't know the actual answer, but it may be that the display actually expects 32bpp, in which case it would be over the limit by a considerable amount.
3 colors * 1 byte * (8 bits/byte) = 32 bits
FYI, Wikipedia's section on DisplayPort lists the resolution of 5120x2880 x 24bpp @ 60Hz as requiring 22.18 Gb/sec of bandwidth, see http://en.wikipedia.org/wiki/DisplayPort#Specifications