I would just go and spend less money on the high flow Donaldson. The QP has a spiral design in it that could hurt exhuast CFM (flow) where as the Donaldson is a true straight through unit (almost like a glass pack, but without the noise).
I'm also wondering what the cfm would be on the qp's ... friend of mine had a set that slipped down inside his pipes .... Im gonna haft to call him to verify his fuel mpg results, but i do remember him sayin turbo spooled quicker?... he sold that truck and moved west , gives me a good reason to call..On GR's web site i noticed that over a certin horsepower they recomend 2 mufflers and size reqiurements ... maybe because of cfm?.. have to call them also.... the donaldsons work very well had a few of those... also tried walker mega flows once they had a really nice sound and flowed well... the mf's were a bit more money than donaldsons dont think ya go wrong with either... just outa curiosity would like more info on qp's