For anyone who uses the Xray x12 here is a list of the option parts I like to use.

#375010- graphite rear axle.
I prefer to use the option graphite rear axle on my x12 to help reduce weight. Reducing the weight at the rear of the car will also make the car easier to drive and more predictable. For stock this also helps as it's less rotating weight to spin.

#930230 - ceramic ball.
To increase the efficiency of your ball diff this option is perfect. The diff on a 1/12 car is a critical part of the performance so making sure it's always in perfect condition is important. These make your diff silky smooth but also have a very long life.

#378071-o shock adapter
This option is used to increase the shock length. I find when using the longer shock the car is a little easier to drive and more predictable over bumps.

#372113/#372012/#372022/#372013- graphite options
The graphite option parts have a big effect on the cars handling. When using the option graphite parts the car becomes more consistent as the front of the car with have less flex and twist. In higher grip conditions this will have more of an effect but is still useful in lower grip conditions.

#372317/372318-o - alu eccentric bushing
The alu eccentric bushings allows you to adjust the front bottom arm to either increase track width or decrease track width. I find making the front end wider on the bottom will reduce a little turn it on entry making the car easier to drive.