The different minecart types and states do not respect an increased minecartMaxSpeed and seemeingly have their own arbitrary speed caps. Aside from being a bug this conflicts with the stated experiment goal of having minecarts with "predictable motion"

Reproduction steps

• Build a long loop like this
  
• Set minecartMaxSpeed to 1000
• Place your minecarts
• Use the /data get entity command to see the speed (try to time it when the minecart is going straight)

Tip: Run /tick rate 200 command for a few seconds so the minecart reaches max speed faster

Observed Resuts (at minecartMaxSpeed 1000)
no_longer_equal.mp4

I'll be listing "bpt" (blocks per tick) speed value from the /data get command

Speed cap "20bpt" - Works as Intended (400 bps which is quite far from 1000 but according to the changelog that's to be expected)

• Minecart occupied by a player
• Minecart occupied by an entity

Speed cap "12btp"

• Hopper minecart
• Chest minecart

Speed cap "4.7bpt"

• Furnace minecart with fuel

Speed cap "2.4bpt"

• Empty minecart
• Command block minecart
• TNT minecart
• Spawner minecart

Speed cap "1.35bpt"

• Furnace minecart without fuel

Expected Results
All the minecarts would respect the minecartMaxSpeed limit as they do at the default speed limit (or at least be consistent with their behaviour at default)
equal_at_default.mp4