Hi Henry,
don't switch on GI Surface Details. AFAIK this renders subpixel level GI detail, and i have yet to come across a situation where this is required. I have recently rendered a (quite normal) scene that took 4 hours on 800x500 resolution, and I wondered why it took so long. I then discovered that I had GI surface details checked by accident.
I've had it unchecked, rendered again and the same image was done in 20 minutes.
As for the "ray detail region" setting: there is more to explain about it but I don#t have the time right now. You should find a good explanation here on the forums though. Generally for a full render just use the default setting "detail in crop region".
Regards,
Frank