Best Exhaust manifold?

[Cuprafenix]

Hi, I'm in search of an exhaust manifold for the williams.

Till now the only ones I saw are from Iresa and KTR.

And also for the rest of the line what do you experts suggest? 55mm or 63mm?

Regards

[diditno]

Ive got a supersprint one on mine, same as ktec i beleive, that with a standard exhaust is fine. Changed it from the original as i couldnt get the join/fire ring to stop blowing.