A tip taken from Associated and slightly re-worded, re: composite V graphite parts...
A graphite part will NOT be stronger than a composite part.
The graphite parts have less flex, which a good driver who doesnt board tap etc can usually find a few tenths of a second using graphite parts at the most.
Composite parts will have more flex, so wont offer an as sharper handling car as the graphite parts, but should be less prone to breakage.
As a side note, alloy parts, although strong, can bend on impact and cause handling issues- So, they are good if you want to stand a better chance of finishing a race with a car in one piece, but they are usually heavier than composite or graphite, and have the possible added downside of making a car ill handling.
I learnt my lesson by tricking a car out with alloy the hard way in my earlier years of racing, as it drained my bank balance, added weight to the car and eventually gave some bad handling.
Now, ususally I can drive a car without board tapping with composite or graphite parts and realise the err of my ways when I had the all alloy tricked out car.
So, alloy might look nice and usually stay in one piece, but thats the only good thing about it...