If she is on the small side, the Marathon click tight might be great for her. It's taller than the previous generation by a little bit. Britaxes get a bad rap for being short shelled, but my average almost 3 yr old will make it to 4 and she's in a G3. So the click tight Marathon should get you a long way.
The head wings are not reinforced with EPS foam in the Marathon. They are more head rests than actual SIP wings. That would be going to a Boulevard, which also offers a ton more height.
For smaller than average I would do the Marathon unless you really do want to rear face forever - like 4+ - or want the extra protection in the head area. The Britax shell is very deep so still a lot of SIP in the Marathon.
If you want the max SIP, the click tight Advocates are a lot less bulky than the the G3/G4 and are great for peace of mind if you have an outboard kid or a car with no airbags.
If it were me, I would buy now because it's safer to rear face at a more upright angle. Less downward rotation and forces on the neck in a frontal crash if you can install more upright than the 45 degrees of an infant seat.
Last edited by flashy09; 11-22-2014 at 12:11 AM.
DD1 9 yrs old 12/2011
DD2 7 yrs old 01/2014