Not one of the mentioned mods to the CR2 makes it harder to drive, they are mainly suspension geometry improvements, which make it more balanced.
Of the above I think the only thing you should definitely have is the horizontal battery strap which replaces the two standard ones. This is more a security option than a performance increasing option though.
The XXX rear end is being used by an increasing amount of drivers, all of them liking it. The only situation where you could benefit from using the CR rear end (the standard one) is when the track is very rough. Like grass tracks at times.
You will notice the big difference when you use the XXX rear end and after a few weeks/months put the CR one back on to test
