Here is one study where Power Service & Howes are in the middle of the pack. There's another report which goes into much more detail but I can't find it yet.
Lubricity Additive Study Results - Diesel Place

__________________
07.5/6.7l, Metalic Silver, 3500 fully loaded Laramie, DRW, TransferFlow 98 gal. in bed aux. tank, PullRite Super 5th wheel, AMP Research Power Steps, Firestone Ride-Right dual control air bags, Bilsteins all the way around.