Luck. I just multiplied the defaults x 2 and kept hiking up the 24H video bitrate until it capped. A 3x multiplier didn't work and a 2.2x didn't change the result so I stopped at 2x. The GOP 3 I've been using for months with 1080 24P Native on the GH1 getting about 48mb/s and very filmic footage. But the GH1 at that setting wasn't stable on death charts, grass or trees. The GH2 is AND at a much higher Mb/s.
These are the most extreme 1080 24P 3 GOP settings I have tested that produce an amazing, filmic image while still managing to playback in cam, computer and ingest into an NLE (still has 10 frame glitch in beginning of clip):
Video Bitrate 24H=65000000 1080i50 and 1080p24 GOP Size=3 Video buffer=0x3000000 Video buffer 24p=0x3600000 1080p24 High Top Setting=42418 1080p24 High Bottom Setting=29692 1080p24 Low Top Setting=31178 1080p24 Low Bottom Setting=21824
(PAL users wanting to shoot 1080i/50 may need to add the following as the above settings force pal 1080i GOP to 3: Video Bitrate FSH/SH=42000000 Video Bitrate FH/H=35000000