Here's a graph of delta E 2000's for 8 bit colorspaces. Included are sRGB, Adobe RGB, ProPhoto RGB, and a linear RGB space.

Gamma of the colorspaces:

sRGB: linear with gamma=2.4

Adobe RGB: 2.2

ProPhoto RGB 1.8

Linear RGB: 1.0

The graph shows the Delta E 2000 for adjacent steps in the 8 bit colorspaces from (0,0,0),(1,1,1),...(255,255,255). For 16 bit images just divide the Delta E's by 256, or 128 in the case of Adobe Photoshop which scales 16 bit images to 15 bits.

There simply is no issue where accuracy at low luminance needs more than 15/16 bits and 8 bits is right at the threshold of observability except for the linear gamma which gets pretty bad at low luminance.

sRGB does a decent job in 8 bits. At least for the tone curve. sRGB's big weakness is it's really narrow gamut. Something that's well explored by many. In particular, Andrew Rodney has extensively gone into sRGB's printing.

All of these, even with Adobe's 15 bit limit, work fine in "16" bit RGB spaces. Even linear, gamma=1.0 spaces which have a max dE00 of .023.