You should be doing this in Compressor. You make a QT movie of your timeline, drop it into Compressor and set up the 3 presets. IMO there is no reason to make QT and WVM versions of the H264. H264 will playback on either platform.
Compressing is something you have to test and get a feel for.
Key Frame: Every...? Leave on auto
Frame Reodering: Checked or Not? Checked
Data Rate: Automatic or Restricted? And if Restricted? If you are wanting those file size then you have to do the math and use restricted
Restricted to how many kbits per second. Simplified 1080p - 1200MB/840 sec = 1.4MB/sec
Compressor Quality High? You have to test but Yes for higher bitrates down to med for lower bitrates