Ok, I have limited my choices down to the Radian or the Nautilus for my soon to be 3 year old daughter (30 pounds, 40.5 inches tall). What I am wondering is, will both keep my daughter harnessed for the same amount of time? I know the Nautilus will provide me with booster after that but at this point I am just worried about the harness mode. Does anyone have any opinion about whether one of these seats will allow a child to be harnessed longer than the other? And if the answer is, they are the same, are there any opinions about which one I should buy? Based on comfort, safety, etc?