Hey Bloggs, I'll take the comment about AUTO METARS, bit pedantic, but taken.
Just with regard to your comment on QNH source. Are you telling me that you would use 'linear interpollation' to determine QNH source from a 2 hour old TAF as opposed to using a QNH from an automatically generated METAR? And do you trust the forecaster to re-issue the TAF in time if the QNH is outside that stated in the TAF?