Another comparison. In this case, out side of a few edge cases, Forward Sentry is better then grenadier vs ranged attacks, however grenadier is better vs melee (given that stealth does nothing against melee). In this case, we actually have an interesting decision to make based on what type of enemies we are expecting.
Graph shows the chance of successful wound given attacker's Quality and weapon AP, highlights show were the Grenadier is better (a few edge cases).
These are the types of choices I think are interesting, were upgrade x is better in situation a, but upgrade y is better in situation b.