well, I guess the question that really needs asking is: "is this an animation or still???" For a high rez still 4,5 or 6 hours isn't too bad. I've had some stills render for 40 hours, of course they are like 10,000 pixels wide and such... For an animation I always render out the irradiance map first. Saves a TON of time.
If I can bring it down to 1 hour per frame, I'm happy. There are things you can do to speed it up without killing the quality. Though I have a small render farm, without that I would be toast.
All I have ever used is maya, actually even before maya it was Power Animator. I love it and it rocks, except for the renderer. It blows chunks!!!!! Maya just added Mental Ray as it's alternative renderer but the GI is horrible. I haven't been able to do anything with it. Lightscape is cool but porting my geometry from maya to lightscape is a bit of a pain. For architectural rendering I don't think maya is the best choice.
