I was just looking at the Power Boost tree. It seems like a fairly cheap way to increase support ship speed.
Going from ion engines to magneto-plasma costs 32000 research.
Going from 0% boost to 20% boost cost 2,000 + 4,000 +6,000 + 10,000 or 22,000 for a 20% boost in power.
Combined, that goes from 60 power per engine to 96. That is a 60% increase in speed or about a 50% increase in cargo and colonists transported per build point.
For boosting support ship efficiency, boosting armor tech, engine tech, and power boost tech is the way to go.
Boosting shipyard speed also helps, because each ship will spend less time being overhauled.