I never got on with all that tone mapping, I eventually found that my renders looked better with it off. I remember having my render settings quite high at one point. I tried doing a GI render with a single V4. I set it going before I left the house at 9am, when I got back well after 4pm it was still pre-calculating!!

You can reach a nice trade-off between speed and quality. My ratyrace bounces are never set above 2.

CHEERS!