Doubt it ratios wil be closer together on a diesel normally some one will give you better understanding I'm sure haha
 
having done it on a 16v i wouldn't reccomend it unless you wanna cruise the motorway on tickover all day
 
so it is better to stick with my 5speed gear box. but is it powerfull for a 550hp car ??
 
in a 550bhp car you will be breaking any and all 02J gbox no matter what ratios are in it I think
 
well right now i have 411whp and 58Kg of torque and still my gear is surviving loll except for the synchro i lost one from fast shifting. so i thought ill install a six speed gear box to make the car more alive
 
I eaten a few gears on my ibiza

2nd, 3rd (twice) and 5th are the kills to date.

02A and 02J boxes

Now using SQS dog box gear set and plate diff.