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Replying to your post is going to take this thread a bit off-topic, but you raise a few valid points that I want to make sure get addressed. I also want to clarify a few things that you said, so that others who have experience with this seat might be able to help you.
First of all, congratulations on the new baby, and congratulations as well for taking the time to research your car seat choices! It's an oft-overlooked subject for new parents, but so very important. I'm glad you came here.
If I understand correctly, the main "selling point" of the Air vs. the regular OnBoard is the "air protect" head wing cushions that are also on the Complete Air. Safety 1st says that the cushions help protect in side impact, which may well be true. There are no side impact testing standards, so all side impact "testing" claims are buyer beware. The great thing is, rear-facing in in of itself has huge benefits in side impact, so additional side impact protection is just icing on the cake.
...but the discussion was that they grow out of the infant seats quickly, and perhaps we should spend on a larger forward-facing seat that could be used for years. <snip> My wife really wants a Britax Marathon when the time comes. I was hoping for a 35 lb seat to keep the baby rear-facing longer since I've heard that they can grow out of a typical 22 lb seat in 6 months. I live in California where the regs requires rear-facing under 1 year even if over 20 lbs.
A couple of things about this paragraph. First of all, and most importantly -- one year and 20lbs is an old minimum for forward-facing. We prefer to see kids rearface for three to four years, with two being the absolute minimum. Research has proven that young children (one-year-olds in particular) are up to five times safer remaining rear-facing. As such, ideally a 'larger forward-facing seat' will be a good while in your future. Typically, we recommend using an infant seat for the first while, and then switching to a convertible that can be used RFing for several years (though a convertible can be used from the start, if you prefer.) Here's a good video that helps to explain why we want you to RF longer...
[ame="http://www.youtube.com/watch?v=Q8gU9zzCGA8"]YouTube- Front facing or Rear facing? Car seat safety TRUE STORY crash test videos[/ame]
We have a handful of seats that we frequently recommend for extended rearfacing, but the Britax Marathon is no longer on that list. The reason for this is because there are several other seats which will allow your child to rearface longer, in weight limit, height, and leg room. Once your baby is here, and you're ready to get a convertible, you can post again and we can make recommendations based on whether your child is tall and thin, or shorter and stocky, and also based on the latest and greatest. (The same goes for a forward-facing seat when you get there.) A year ago, there was not a single seat that went past 35 lbs in RF mode. Now there are three 40lb seats and two 45lb seats (though both are different models of the same seat,) with two more 40lb seats soon to hit the market. These things change quickly!
As such... it might do you well to purchase a smaller, less expensive infant seat, and then spend more for a good ERF seat. There are ERF seats which will last a long time for RF, and then a long time for FFing, leaving you to only need to purchase a booster when the time comes (at age 5-6.) Or, if you plan to have more children, you can pass down the ERF seat and get a dedicated FF-only seat that will eventually turn into a booster.
Now that I've thrown all of that at you, I want to try to address your original question at hand. As I said earlier, I do not have experience with this particular infant seat, so hopefully someone who does will correct me if I have misunderstood something.
The reason that an infant base has different reclines is primarily so that it can fit different vehicle seats. A seat that is very sloped will need the recline foot lowered; a very flat seat will not. What you are attempting to achieve is a 45* angle for a young infant, so that his/her head does not flop forward and his/her airway is maintained. So, if you are able to maintain this angle without putting the recline foot down, this is just fine.
In the long-term, if you are not able to get it into the 11-35lb angle, that is not really a problem per se. Older babies/children might prefer a more upright angle, but it is not necessary for their safety. Acceptable RF angles range from 30-45*, with the 45* being necessary for a newborn. There are some tricks that might be useful in terms of getting a more upright angle, but I find that many parents simply opt to switch out of the infant seat and into a convertible (which can easily be installed more upright) when the baby desires a lesser recline angle. As such, I think that rather than spend the extra money on the base, I would save it and plan on putting it towards a nicer convertible, since it is unlikely you'll actually need to get a more upright angle as early as 11lbs, since an 11lb baby is likely to still the support from the 45* angle.
BTW, what vehicle are you installing this seat in, and are you installing it with the seatbelt or with LATCH? Many vehicles prohibit using LATCH to install in the center, which is why I ask.
I know that was reallly long, but I hope it gave you some insight and answered your questions. Please feel free to reply back with any additional questions you have, or any clarifications you might need (I tend to get wordy sometimes!)
