About Cortex Implants, it says that common quality ones give a 1d10 penalty to WS / BS / Int, but what about Good or Best Quality one ? What's the point of getting Unnatural Intelligence if you get reduced Intelligence from the Implants themselves ? It's kinda like shooting yourself in the foot.
Oh and earlier someone said he had as much as 78 Intelligence, how do you do that in RT ? Most I can see is like 70 (25 base + 20 roll + 5 background + 20 XP).
Good quality CIs do not reduce stats. It gives Unnatural Intelligence (x2) and the recipient gets 1d10 IPs. The WS/BS/Int modifiers only apply to normal CIs. The RAW does not say anything about Best quality, but a houserule could be to remove the added IP and even reduce the total IPs accumlated and/or Unnatural Intelligence (x3).
Typically, Best Craftsmanship implants don't offer any game mechanics advantages over Good Craftsmanship implants. Those that do will specifically say so in the description. What Best Craftsmanship gives you is more aesthetic appeal - either with more frills and shiny bits or by being totally concealable.