If you wire the valve open, you`ll have a big flatspot under 3500-4500 rpm.
If you get the exup free headers, expect to do a little re-jetting.
There is quite a weight saving with the new headers, about 7-8kg if i remember rightly.
I have them fitted to my Ace, but the cam overlap is different between the Ace and YZF`s, so theres no need for re-jetting the Ace.
The only reason i fitted them was the Ace headers are made from cheap metal and rot quickly, and theres no need to worry about servicing the exup valve.
If you don`t mind servicing the valve, spend your money elsewhere as i don`t feel theres any power gains with the new headers.
And if you have flatsides on your SP, might be a nightmare setting them up correctly?