Unfortunately-
Unlike automobiles, it is very hard to use crash test results to compare child restraints. Fit to child and vehicle is very important, and what works well for a dummy and flat bench test sled may not fit the same for your child and vehicle. Also, without any correlation to risk of injury, it is very hard to tell how much safer one seat is than another. Finally, keep in mind that most injuries and fatalities are caused by non-use and misuse of restraint systems. Differences among properly installed and used child seats of the same type are not very large in terms of safety.
You should choose a carseat that fits your vehicle well, that fits your child well and one that has ease-of-use features that will allow you to use it correctly each trip. I suggest our guide to carseat features,
http://www.car-safety.org/guide.html . In addition to giving a brief list of features, there are also links to buying guides including Consumer Reports which does have some crash test data.
There may also be some information on this in the forum archives. I found this thread on a quick search:
http://www.car-seat.org/showthread.php?s=&threadid=799
I hope that helps!