Inter-thermal Speed To Fly

Morning,

I'm reviewing some STF topics to correct some fallacies that seem to
have crept into my understanding of STF theory and application ... I
though I knew this stuff ... or maybe I forgot ... I am a senior now,
you know ... :-))

So, if I have MC set at 3 ... and I am crusing XC to the next three
knotter ... should I slow in lift and speed up in sink ... or will I
have a faster average speed if I just hold speed steady ... i.e. at
the velocity appropriate for MC = 3 in still air. I see pilots doing
both ...

Also, do all flight computers compute inter-thermal STF with the
formula that does not include a wind component - as identified in
Reichmann's texts, for example.

Anybody have an excel program that will plot polars ... including the
tangent to the shifted origin you get when when you change airmass
sink ... or tail/head winds ..

Gracias, Happy new Year ...
KK