The fact that the VRayMtl Bump value is set to 30 is the same as for 3dsMax standard materials and physical materials, but in recent PBR workflows, it is increasingly set to 100, and it seems that the default value should be 100 already, what do you guys think?
Arnold Standard and Corona Physical already appear not to be 30% default.
I would like to know this too…i still leave it at default 30 at the moment…
Here is a post with some answers 
Why is the Bump Map set to 30% by Default? Why not 100% - Common :: Render Theory - Chaos Forum
This is an issue that depends on feedback from many users.
Searching the forums, there are few queries about problems with Bump 30%, so many users are fine with the traditional 30% set-up.
Only minorities with PBR setups (mainly mapped from Substance) have an opinion on this issue.
（I use Substance Painter, probably a minority.）
Chaos will not review the 30% setting unless there is input from many other users.
That is why I have put my opinion here.
My thinking is that it can be viewed as mainly subjective.
Where a bump/normal map has been derived from a specific model/material made with some specific software, i.e. Zbrush, Substance et al, I would
suggest that a value of 100 is correct insofar as that was the ‘intended’ effect and designed to mimic the high poly model as closely as possible, with any lesser value being for personal reasons or for use of the map outside of its
intended situation, as a blend with others perhaps.
In the past mostly, (and where appropriate or the only option nowadays), bump maps were/are mainly guesswork/artistically perceived versions of the diffuse, so any arbitrary value could be used, so 30 seems to me just a random value
someone chose, based on who knows what at he time
That said, if it were a poll then I’d say default it to 100 and claim ‘modernity’ 
to be fair, the 1.0 (100%) that it defaults to in Maya is ALWAYS way too high…I dont know if the 30% is the same in max, but I never use bump value at 100% in maya. Even subtle maps look weird at 100%.