MM5.5, I agree with having the FMS do these calculations -- if only we can get the certification authorities to get their heads around it.
In fact, it seems that laptops with manufacturer sanctioned software is an end run about the certification bureaucratic hoops involved with putting these capabilities into FMS.
Introduction of laptops into cockpit performance calculations seems to have increased the proliferation of information sources already populated with FMS, performance charts and ACARs -- and has introduced more ways to get things wrong as we have also seen with MK in Halifax.
If the crew is expected to dash off a quick critical calculation in a compressed timeframe, they need a straightforward SOP that perhaps excludes unneeded bodies / distractions in the cockpit while this is being done.
42psi, both time and distance to 80 kt. (or other speed if necessary) are equally valid for performance monitoring, but I don't think we will see distance boards put up anytime soon and stopwatches are readily available.