I'd like to know, are there gecko codes that make certain CPU(s) better/faster than t

[Vega]

Looks like your title got cut out at the end.

You can effect the CPU speed limit with this code - https://mariokartwii.com/showthread.php?tid=2219
You can also force the CPU difficulty with this code - https://mariokartwii.com/showthread.php?tid=2220