Go with the two piece. I got a one piece and would have had to buy a NEW 2-piece if I got a speed kit.
Like the others said the 2 piece can be adjusted for more speed or more power... kind of a neat trick for 'fine tuning'
If you get a biturbo-- DONT FORGET to get a side mount kickstand. I didn't know this, and my center mount stand would drag everywhere--- the pipe prevents it from retracting properly.
I don't want to see you all exited about your new exhaust, only to hear metal scraping on every corner.
Not to mention, that kickstand could 'catch' on something and you'd probably dump hard.
Just an FYI-- I'm interested in the Techno Pipe.... let me know if you go that route.