My Tall 3 1/2 y.o. daughter stay in Marathon or get Regent?

[Boogiemama]

My Tall 3 1/2 y.o. daughter stay in Marathon or get Regent?
I am getting a Regent for my son (5 1/2). My daughter 3 1/2 is in a Marathon
now, about ready to move up to the last notch, she is tall.

Are the buckles more secure in the Marathon than the Regent for someone her size (3 1/2)? Should I keep her in the Marathon for another year
or go to the Regent (which sits lower in the car).

The main reason I am asking is that we bump her head on the door frame
roof sometimes when I pick her up and put her into the Blazer, especially when she is wiggly. Lately when she is cooperative I let her climb into the Marathon herself, but sometimes she is fussy or tries to climb over to the back to get something when we are late for preschool, typical 3 year old stuff.

Despite that, since we love love love the Marathons, we can keep them, but should we get a Regent for her now while they are on sale? I have relatives who will love the Marathon if I give it to them. We are definitely sticking with 5 point harness seats.

http://youtube.com/watch?v=azgBhZfcqaQ&feature=related