I've whittled my car trial list down by going to the car content tab in content manager, pressing "alt-a" then removing the ones that have fewer than 4 LOD's, too many triangles or no HR cockpit. It has really cut down on my time by weeding out the cars that don't have what I perceive they need.
At this point, I've downloaded soo much content over the years for AC that I've decided to keep only the very best that I find. There is just too much space taken and also a confusion of content. There is soo much content that there is no direction for me. In a perfect world, even one flaw and the car or track is gone. Realistically though, that's not a mentality that I can stick to!