[mythtvnz] HDD Space Consservation - 1080i DVB-T vs DVB-S 576i vs ?

[Tortise]

Given the recent changes of TV1, 2 etc to 1080i we now have very large files from most recordings.  With TV3 if one didn't want a HD 
recording one could just record on TV3+1 for a (much) smaller file.  While I am not using a 1080p 52 inch display the difference 
between 576i and 1080i is frequently minimal, (although obviously superior to SD.)

A brief file size comparison tells me we are talking about less than 2G (one hour of 576i) vs. over 5G (1080i) which means 576i is 
typ 40% of the 1080i files.

This means potential of over twice the material on the same HDD.... which seems worthwhile...

One way to get smaller TV 1 and 2 files is to pull them down over DVB-S.  I guess this can be done but might be interesting to setup 
so that one could choose the preferred file size.  For example movies at 1080i might be desirable, while much else might be ok at 
576i.   Anyone tried to select TV1/2 recordings based on the file size they want?

At a guess an alternative might be to transcode the recorded 1080i files to 576i or maybe 720p I presume as a user job(s).  Is 
anyone using this approach?