We are running some testing for EXRs rendered from Clarisse 4.0SP1
Here are some stats, rendering @3424x2202 and using 23 AOVs (PBR, Cryptomatte and 2 Utilities):
EXR (ZIPS compression) - 300mb per frame // single AOV using split AOV preference
EXR (ZIPS compression) - 750mb per frame // Multi-channel exr
EXR (ZIPS compression) - 160mb per frame // Multi-channel exr // Half res
*ZIPS compression I've found unusable in Nuke, it will crash or be extremely slow to use
EXR (ZIP compression) - 32mb per frame // single AOV using split AOV preference
EXR (ZIP compression) - 370mb per frame // Multi-channel exr
*Going above roughly 8 AOV's becomes sluggish in Nuke, as it does with any large EXRs. As there are so many AOVs needed for cryptomatte we have split our renders into two, one containing crypto and utilities, the other containing the beauty and PBR AOVs