No matter what settings I have in config, the cart not running faster than 30 b/s.

This is an internal issue with the way carts and rails interact. I can try to force my rails and carts to use a higher speed, but it may lead to weird speed bugs and how chunks load.

It will be nice to try that, at users own risk :). I've seen a bukkit/spigot plugin called train carts. It enables speeds up to 100m/s, but you can barely see surroundings. This plugin also alters cart physics.