I've had a 28 volt Milwaukee set for several years, and have been extremely pleased with it. The torque on the 28V impact is impressive - much more so than the 20V models. Usually I toss it in my truck (F450) when I'm making a cross country trip with atrailer (in case I get a flat). Beats the heck out of humping on a lug wrench! I don't think that it would remove the lug nuts on a logging truck though...
For all around construction and electrical work around the farm, the 20V sets are nice because they are smaller and lighter. But for a true workhorse, the 28V is hard to beat.