Hi
many questions at one time.
Usualy, when you use the 1.09 version of Vray, and also with 1.5 and also with max radiosity system, you will not have the possibillity to realy simulate real world light distribution because of several reasons.
first of all, you don´t have the real world parameters, of material light reflections. those are more complicated as it seems. Max radiosity overrite mat goes a step ahead and alows to give the overal light reflection value in % steps, which gives you a bit more of control. Vray only gives you a way to do this via rgb values or Gi multiplier, which is wrong at last, compared with realworld parameters and also dont give real control. Also, light reflection to a scene is partial diffuse and partial specular, which means, only highend lightplaningsystems like “spectar” or for example “radiance” alow such materials and also alow realworld lamps with an energy amount. At last if renderers like these are able to calculate the relistic energy distribution, they still have to deal with the problem of transforming them to a rgb valu on your screen, and at last here, they have to deal with all the problems, a photograper has, because a screen can´t display wether the wavelength of light of realworld, not the differences between brighter and darker areas, as realworld does. So all of them have some sort of exposure, to translate energy values to a predictable screenbehaviour, as one would expect it. (This is why it is only called photorealistic and not realistic)
OK i think this doesn´t help you so far, but shows, that realworld lightsimulation isn´t the total aim of renderers like brazil, vray or finalrender. They have the aim to make nice and fantastic images very fast and intuitiv, and nothing more.
So with 1.09, you might use photonmapping to solve a bit your problem. I-map calculation as you might know, chooses (very intelligent) single points in your visible image areas, and only at these points calculates the incoming light. This hapens by trycing a bounce of dozensz of secoundary rays away from this point, to see spots of light around this first point.
When you render an interior, usualy, you get less and smaler areas with light,compared to exteriors, wich means for the i-map calculation, that you have to trace many many more rays, to hit statisticaly correct those smal areas of light, and this also is the reason, why i-map calculation is usualy much slower in interiors as in exterior renderings, where you have much more bright areas, to be seen from your samplepoints.
photonmapping tries to solve this problem. It shots virtual photons away from your lights, that hit the surfaces, lose energy, bounce to the next walls, and by hitting, bouncing, and loosing energy very fast can make an averaged lightsimulation of your overal lightning.
this is calculated very fast, but can be quite difficult to be tweeked with so many lights.
But this way, your secoundary bounces are calculated very fast, and your imap takes this allready good overal lighting and now has to trace much less rays to get an god aproximation to the real light distribution in your scene. with this method, you don´t anymore need quasimontecarlo for secoundary bounces. photonmapping can speed up scenes between two to three times in interiors.
(you can find a good tutorial for Photonmapping when you look in the announcement section. Vlado has posted a link to the new internal textes for 1.5, and there is also the tutorial section)
you also should see, if you use softshadows, and how low you can get with your softshadow samples settings to still get good rendertimes. (many softshadows can be a timeeater).
at last, if you use many softshadows, don´t try to use analytical antialiasing (adaptive subdev), but simple two level. the analytical cant deal that good with al those pixel based effects like soft shadows, and very smal details the analysing process here can get slower than the rather brutal antialiasing effort of simple two level. Simple two level, in such a case can make renderings two times faster.
OOps, i think i´ve just written a book. :shock:
Hope there´s something that helps you 
Tom
