like BB said., in reality nothing is 100% bright. 0,8 is a good number. diffuse 1 is 100% the texture. if you set it to 2 it would be superbright. to bright IMO.

That would be correct if the shader was working correct, but if I'm not mistaken BB agreed that some work had to be done on the eye shaders, because the default poser A0-node darkened the eyes too much. You're talking about reality but in fact a shader is a approach to create reality. Sometimes nodes in shaders need values that go beyond what is supposed to be reality. You have to play with the settings to get a "realistic" result, and now and then you have to break some rules. What only counts is the result of the rendered image and you need your eye to judge if it's realistic or not.
When I set up a scene I start with some default settings: on the shaders, the lights (IBL, fill-lights, rimlights etc) and make a testrender, and then I start to tweak everything: a little more IBL, a little more shine-spread, a little less diffuse etc. etc and I don't care if the nodes are not set as they are supposed to be, and I make literaly dozens of renders untill I'm satisfied.
This doesn't mean that I'm very impressed about Baggingsbill VSS and it's shaders and his huge knowledge about poser's material room, I have used VSS from the very beginning and I use it in every render since.
But there is more than VSS to make a good and realistic render, if you have a lousy skintexture or eyetexture you will have to tweak the VSS-shaders in all kinds of way to get a satisfying result. And the same counts for IBL-images. And of course there is firefly, which doesn't always behave as we expect.
VSS is a cookbook with a lot of good recipes, but sometimes you have to change some or add some for your personal taste, and if you don't have the good ingredients the results won't be what you expected.

best regards,

Bopper.

-How can you improve things when you don't make mistakes?