I encoded a 1920 x 1080 clip into m2v and one as h.264. Two seperate export files. One hour 15 min created 6 GB H.264 and 15 GB M2V.
I had great difficulty distingushing any differences between the two viewing the videos in Adobe Encore. The video is a dance recital. Stopping both videos at the same frame and comparing the two proved indistingushible. However, motion in the H.264 seemed pixleated, not as smooth as the M2V version.
The bit rate settings for H.264 was approx. 16 MBPS , 30 MBPS for M2V (these were the max. Values possible).
How can you compete for fine detail when you are only 16 MBPS and your competetor is 30 MBPS???
Food for thought....