IXIL, Musarri or Screaming Demon Silencer?

[Mincehead]

To be honest MOST straight through absorption type cans will perform within small percentages of each other but yes, tuned lengths of exhausts are important to keep the power and torque characteristics you may be after.
This MEZ porting table may be of use to you:

http://www.mez.co.uk/mezporting/exhaust_length.html

Good luck with the `science`.