I have no expertise with configurable speedboards ... but if you hop on Skype IM, I will be able to direct you, with what you want.
The reason I use invisible speedboards by Biddle, is because I need not see a barrage of different visible speedboards, when invisible ones are available.
I was using CSX Speedboards, but my trainz were clipping the signs, and some signs were in the gauge, and fouling turnouts ... invisible speedboards solve that problem greatly !
Some of the 5 kph, 7 kph, 8 kph, and 10 kph metric speedboards, achive a slower speed, than a 10mph Imperial speedboards.
I adjusted my speedboards so that they are visible (for easier movement around in surveyor), by eliminating the surveyor-only config file tag (I can always put the tag back i again to make them invisible).