All car seats must pass the same safety tests, so all car seats are safe provided they are appropriate for the child's age and size and are installed and used correctly. Car seat manufacturers are responsible for their own testing and very few, if any, release there figures. Britax do not, so we don't have much to go on.
What sets Britax and some other car seat manufacturers apart is their ease of use features. Britax has built-in lock-offs, easier to use LATCH connectors, EPS foam, non-twist straps and higher weight limits that make their seats easier to use correctly every time, then they may well have an edge over competitors. Britax also have seats that have side impact protection and have been tested for side impacts. The new SafeGuard seat manufactured by IMMI also has these features and has been more forthcoming with their research results. They even have their crash test videos on their website:http://www.safeguardseat.com/child/index.htm
All car seats do a wonderful job at protecting babies and children. Children that are killed in crashes are more than likely not in a car seat or in an inappropriately used car seat. Of course there are some crashes that are just not survivable whatever car seat a child is in Britax or not.
So the answer to your question is no, there is no research that shows Britax perform better for smaller kids or any kid for that matter.
FWIW, here is my best practice:
RF for as long as possible, ideally until two years old, three or four even better:http://kpho.static.worldnow.com/imag...safetyseat.pdf
Page 5 is quite compelling...it really shows that every step UP in car seats is a step DOWN in safety. So if you all ever feel we car seat geeks are harping on about RF being so important or not putting kids in boosters till at least age 5+, well, at least there is proof now>
Of course, this study only shows rearfacing and booster seats, not forward harnessed seats...but taken together with this study from Australia, which finds top tethering to be a huge safety advantage in harnessed FF seats, I think we can put together a pretty good 'best practice' scenario for all our children:http://www.aaa.asn.au/issinfo/crs_ef...eness_13pg.pdf
1. Rearface to the limits of a good convertible seat (at least 30 pounds, depending on the seat, and top of head roughly even with the top of the seat shell... should be age 2-3 for most kids)
2. Harness to the limits of a forward facing seat (40-80 pounds, depending on the seat, shoulders not above the top slots, ideally seats with short slots (14-15 inches) should be replaced with taller seat (17-20 inches) for kids younger than 5).
3. A good highback booster (why highback? They reduce head injury by 70% in side impact crashes compared to no-back boosters http://www.eurekalert.org/pub_releas...-htb090905.php
) until the child is too tall or heavy (57-60 inches, 80-100 pounds, depending on the seat, usually at least age 10-12 before a child fits properly in an adult seatbelt, depending on the car and the child).
4. Sitting in back till at least age 13, preferably older, because airbags are hazardous to kids throughout the early teens http://www.yourlawyer.com/practice/n...bag%20Injuries