I have never spent the extra dollars to get mandrel bent pipes because the benders around here couldn't be bothered. I honestly don't know if it is worth the money. I would go up to 3" regular bend to get more flow. If they were the same price 2 1/2" as compared to 3" non mandrel I think I would pick the 3" regular only because I think it looks nicer and nobody seems to care what bend the pipes are anyway. At any rate gains will all take place at 5000+ rpm so I doubt you would notice a few extra HP at this rpm level. I don't know if it is worth the money, I kind of doubt it.
Outlawed tunes from outlawed pipes