[Suicide Junkie]

Originally posted by aiken:
I guess that initial question was different - how to make AI to design Frigates (for example) with same or slightly better amount of movement in early, mid and late game stages.
I think the only solution will be to use Misc Ability SPO instead of Minimum/Desired Speed (as SJ said), coupled with engine mounts.

Er, min/desired speed should be used with mQNP, and Misc abilities should be used with regular QNP.
You can mix them a bit to change the design's speed for different hull sizes, though.