Not trying to dampen your spirit but i dont think there is any
'super' part out there that will make the EG6 or any other car that
much faster or better. If you observe the battles that people have
been playing, the car that wins most is the person with the most
driving skill and usually, their car is not that different from any
other. I have seen people with less than 100K points DC2 beat a
fully mod DC2 driver.
Most upgrades through parts change are external modifications and
once you get 990K points, your car would have been fully modified.
Which means, it is as fast and as good as it can possibly be.
Further enhancements would depend on the parts change that you feel
good about.
Perhaps you can change your body to carbon fibre elements (bonnet,
mirror, etc) that may lighten the load on your car but personnaly i
am not sure if it will cut seconds of your time.
I have a few friends who owns fully mod EG6. 1 with Tune A and the
other with Tune B. Both of them can do 2:40 consistently on Irrou.
And also post very competitive (quite similar) times on Myogi wet.
However, 1 of them suck on Akagi... 
So i guess you should just change the parts that you like and make
you feel good while driving it. There may be trial and error
involved to find the parts that are suitable for you and your
driving style.
Hope this has helped.
