You got me curious so I looked it up, here's the code for the hoverboard, it seems you reach max speed at level seven but I can't see anything about what that speed is.
<?xml version="1.0" encoding="utf-8"?>
<base>
<Current_Tuning>
<kRouteRadiusToPickUp value="0.5">
<!--Distance away from the hoverboard that the sim will route to in order to pick it up.-->
</kRouteRadiusToPickUp>
<kMinimumDistanceToUseHoverboard value="10">
<!--Minimum distance (squared) of a route that a sim can use a hoverboard.-->
</kMinimumDistanceToUseHoverboard>
<kHoverboardMedatorInstanceNames value="hoverboard">
<!--Comma-Separated List of Hoverboard Medator Instance Names that will be used when giving random hoverboards-->
</kHoverboardMedatorInstanceNames>
<kFallChance value="75, 65, 55, 50, 25, 10, 5, 0, 0, 0, 0">
<!--Chance of falling at the end of the route, from level 0 to level 10 of Future skill. Percent (0-100)-->
</kFallChance>
<kTrickChance value="0, 0, 0, 0, 0, 0, 0, 40, 55, 70, 90">
<!--Chance of doing a trick at the end of the route, from level 0 to level 10 of Future skill. Percent (0-100)-->
</kTrickChance>
<kAdditionalFallChanceIfClumsy value="15">
<!--This is added to kFallChance if the Sim has the Clumsy trait. Percent (0-100)-->
</kAdditionalFallChanceIfClumsy>
<kFunGainPerRide value="2">
<!--Every time the Sim gets on a hoverboard, their Fun motive will increase by this amount-->
</kFunGainPerRide>
<kFutureSkillLevelsNeeded value="0, 4, 7">
<!--Future Skill Levels needed for Low, Medium, High Skill - determines profiency / speed of using the hoverboard - PAB-->
</kFutureSkillLevelsNeeded>
<kFutureSkillGainPerHour value="75">
<!--For every Sim hour a Sim spends on a hoverboard, they will gain this many Future Skill points-->
</kFutureSkillGainPerHour>
</Current_Tuning>
</base>