still think the 2013 is king, I have not and I dont remember anyone else trying the 2039 on here yet. I owuld stick to what works, SO far myself an many others have done a lot of teseting on pipes for the b5, Myself KORTZ and many other still like the 2013 best and 2057, and a lot of guys like the 2035. I would stick with one of those. Since theresults are going to be good. BUt also its personal preference, myself on a truggy I think the 2013 especially is THE pipe, becasue it is much punchier and powerful of the group on bottom end than the others and still has I think the best top as well,...Its a great enigine you will love it!