I disagree with your statements that all carseats are equally safe, because they passed the MINIMUM US safety standards in order to be on the market. For instance side impact testing isn't even a standard in the US, but some manufacturers have designed and tested their seats for added side impact protection, use higher quality energy absorbing foam and reinforce their seats with better construction and features like ARB. Unfortunately there is no way for consumers to have information on how different seats perform under crash tests and different crash mechanics and real world conditions. The only independent agency that crash-tested seats, Consumer Reports, came under fire for their last safety study because their testing methodology did not hold up to scrutiny and was reportedly at much higher velocity than reported.
My personal preference as far as assurance of safety is to choose a seat from a reputable european company. Sure their US models are different that what is sold abroad, but I believe the engineering and construction is based off their european engineering which is held up to a higher standard.
I've used the Chicco keyfit 30 infant seat (it's ok, I don't love it) and currently use the Peg Perego Convertible for DD.