This is very encouraging news. While reading up on the substream setup, somewhere i got the impression that this lead to a necessary loss of resolution but we just had to accept the trade off.Actually using sub streams causes the sub stream to be recorded alongside the main stream in the .bvr file. So it does increase your file sizes somewhat. Unless you record to a different format than .bvr, which is not recommended.
I know that it CLEARLY made my little PC suddenly viable, now, whereas before it was completely garroted.