I am not too much of an expert on this myself.
You might want to ask what they think to the folks at Compressionist forum
http://forums.creativecow.net/compressiontechniques
specifying the software you use for the encoding and the purpose of the end movie (why you want an H264 at that res for, eg for website display...) - and that your source movie has a lot of motion blur.
Typically I am under the impression that for mpeg, noise (by extention everything that has noise like properties like waterfall) is worst then motion blur for an encoder.
If you look at the levels chart here:
http://en.wikipedia.org/wiki/H.264
You will see that bitrate affects the number of blocks used to encode images. For the resolution you discuss, I think I read from the chart that at least level 4 is recommanded (over 20 Mbit/s -- 4 times more then what you said). The strange thing I noticed is sometimes using higher bit rate produces smaller file size. We here have only been successful for our purposes using QuickTime PRO on the MAC with Best Quality without touching anything. On Windows someone recommanded Tmpeg Encoder Xpress 4 but I have not tried it yet.
Pierre
