in Find file dialog box advanced tab why not change file size filter from
File size [=,> or <] [Value] [Byte,KB or MB]
To
File size between [Value1] [Byte,KB or MB] AND [Value2] [Byte,KB or MB]
Or
File size between [Value1] AND [Value2] [Byte,KB or MB]
just like Date filter
this will help to find files in specified range

http://www.ghisler.ch/board/viewtopic.php?t=2786
Thanks