I vote for Vanderlinde also...
I apologize if someone already referenced this article, but if not, check out this before and after dyno run by Jeff Bloor @ Cycle Max, and the CMG diaries as they race a 1100s.
http://www.cmgonline.com/racing/CMRRG/RaceDiaries/Part3/index.html
Here is an excerpt from the article.....
"Wow, this was looking good! Right from the base point and all the way to redline the power and torque curves (almost) remained above the stock ones. According to Jeff, aftermarket pipes usually sacrifice something, somewhere for a gain up top.
There's a significant gain in torque between 3400 and 4800 rpm (with a slight dip at 3800, but a peak gain of 4 ft.lbs.) and then again from 5200 rpm all the way to redline, where it parallels the standard curve, but with a healthy 3 ft.lbs. increase.
Significantly, the max power gain of 7 hp comes at redline, which means that we can now pretty well rev it out before changing gear, without any noticeable power loss. Peak power is up by 3.2% (to 90.5 hp - for the Squids you understand) and peak torque is up 3.8% (to 68.9 ft.lbs.). Excellent.
We were happy and Jeff was suitably impressed. He's tested a few pipes before and reckons that the pipe is a much cheaper option than you would have to do in motor work, to get the same results.
Go Vanderlinde!