x30xe vs c25xe perfomance difference..spoiler identification

[foler]

I am ex owner Cali V6 C25XE. I now have BMW M3 E36 but will go back to Cali V6. C25XE is very nice engine but after m3 I want little more power.
I have questions for some with first hand experience:
1. How much faster is Cali with x30xe vs C25XE?
2. Fuel consumption is the same? My ex cali use 35mpg (8L/100km) with 100 mph driving speed on highway. In the city 19mpg.
3. Any problem with overheating x30xe in Cali?
4. Do I need any other parts than block+heads from x30xe?
5. Which is best diff/transmission ratio for this upgrade? F25 is nice because I dont need to change gear often but is maybe little to long geared. F28 is expensive.
6. Which is this trunk spoiler? I can find it on net.

thanks

Pictures my old car: