I have the Britax Frontier 85, and we love it! We take at least 2 and sometimes up to four 12-14 hour car trips each year, from IL to WV and TN, to see family. She was always uncomfortable in her cheaper car seats, so we had her in a Britax Boulevard until little brother came along, and then moved her to a Cosco 5 point to belt positioning booster....she could never reach the cup holder well, and was just uncomfy....so we ponied up the money to et the Frontier - we figured it will be her last seat, so it is worth it. The seat padding on the butt is much thicker and more cushioning for her little tush on long rides, we haven't had issues with the straps twisting, but we loosen and tighten each time we get in and out, to make sure they are fitted right....she LOVES being able to reach her 2 great cupholders, and so do we! We plan on getting another frontier once the little guy out grows the Boulevard.
I did look HARD at the Graco Nautilus, BUT the one major drawback it that although their 5 point harness says it goes to 65 pounds, but at the time we tried my daughter in it, she was a small 32 pounds, 3 and a half years old,and the crotch strap was at the biggest position, and was already tight. I also read somewhere, that though they say 6 5 pounds for the harness, they only approve the Latch system to 45 or something??? I am not sure where I saw that, or if it is true?
I love our frontier, and you can use Latch to hold it in the seat even after they are out of 5 pt. and into belt positioning booster mode.
I say go for it - really, can we put a price on our kids safety, Britax has a great track record, and I do believe in some things, it is true, "You get what you pay for." - and more expensive = better in some products.
Good Luck deciding, I know it was a long researching process for me, between Britax, Sunshine and Graco.
Jessie P.S. here is a great place to do some research: http://www.car-seat.org/