Alright, let's report some statistics.

If you're curious, I built this scene in 90 minutes.

I am rendering on an I7 4 core dual threaded machine (so C thinks it's 8 heads).  It's a 2.1 GHz with 4 Gig RAM.  My machine is actually an ASUS gaming laptop (It's what made sense when I was living in my beeny apartment in Japan.

The first image I rendered was with just the one light (the distant light) and the skylight.

There are other important things to consider.

I am running with soft shadows set to best.

No interpolation in the GI rendering settings.

0.5 pixel accuracy.

Best antialiasing.

2 pixel shadows

Best GI at 2 pixels

So yeah, this render is basically jacked up to the maximum.

The first scene rendered in about 70 minutes.

The second render adds the three ceiling lights.  These lights are ring lights surrounding the pole from the ceiling and setting inside the "bowl" of the light such that the lights are only able to hit the ceiling.  This pushes all of the light contributions down in the room to be from indirect lighting.

I also felt that 400 on the indirect lighting was blowing out the render too much so I turned it down to 300.

So, the second render is with four lights and the skydome.  It took about 2.5 hours with everything jacked up to the maximum like before.

Other things to consider:

If you put something in this scene which has any significant surface texture (bump stuff), it's going to cost you in render time.  The more objects you put in, the more the precalculations for the lighting seem to take.  With four lights, the shadows also become more cumbersome.

I should also mention that I actually have glass in my windows with light through transparency on.  If I simply got rid of the glass, I would probably reduce my render times by 25%.  I have reflection turned on and that means that C has to render things from multiple angles to get that reflection working.

-Kix