There’s no reason I can think of that would prevent you from matching the file size of the 1080p files on Apple’s site.
Keep in mind your source is interlaced and Flip4Mac’s deinterlacing is very simple. I’m sure Apple’s sources are all progressive. I don’t think Windows Media 9 will look as good as H.264 at the same data rates. On the other hand VC-1 (Windows Media 9 Advanced) should be competitive and will be supported in the next Flip4Mac release. Regarding H.264, Compressor now has very good (and very slow) deinterlacing.
BTW if you are using the Sony V1 why not shoot in 24p or 30p?
Again keep in mind you’re coming from heavily compressed MPEG2 (HDV) and that’s a CBR encode too (as compared to XDCAM which, while GOP based, is a VBR encode). There probably are other related factors that may have impact on quality I’m not thinking about at the moment.
That said, you should get a pretty good looking encode. If you can put one up and post a link maybe I (we) can have a look at it.
BTW, the Apple full size 1080p movies trailers play in real time (progressive download) for me even though they’re around 10mbps. I’d thought I’d mention that, as a result, I’m really a lousy judge of how patient people have to be.