Call me old fashioned but we just use VNAV path and speed intervention if it has a problem, although with geometric path software it usually keeps up. Of course, the forecast descent winds and cruise winds need to be input, but all this calculation stuff.. nope.. even if we get " direct" to its no problem to review the remaining time and convert that to a ROD... strangely, the latest Co-mail advice is not to " try and do a better job than VNAV" applies to climb and descent. Speed brake is hardly every needed,, and it's not a " handle of shame" otherwise it would not be fitted in the first place!