i wouldn't obsess with your A1c of 5.5%, as a) this is already an excellent value for your age, and considering where you're coming from, and b) A1c isn't that reliable anyways, as it can be influenced by many co-factors (like life span of your red blood cells etc). measuring your pre- and post-prandial blood glucose at home (before, and 1h and 2h after a usual meal) will tell you much more about how you are doing exactly. basically, as long as you level never spikes above 140, you're doing great.
the following blog posts from thehealthysceptic are covering this topic nicely as well:

• http://thehealthyskeptic.org/when-your-normal-blood-sugar-isnt-normal-part-1
• http://thehealthyskeptic.org/when-your-%E2%80%9Cnormal%E2%80%9D-blood-sugar-isn%E2%80%99t-normal-part-2
• http://thehealthyskeptic.org/how-to-prevent-diabetes-and-heart-disease-for-16

also be aware that after going very low carb for some time you become somewhat insulin resistant as a normal physiological response to the carb restriction. so don't be surprised if your blood sugar goes higher than expected when taking an unusual amount of carbs in your meal for the purpose of testing. if this is the case, you can subtract 10 points from your level to get closer to the "real" level (meaning, to the level you would have when properly carb-adapted after doing VLC). but again, YOU ARE DOING AWESOME! no need to worry at all as far as i can tell from your info.

First of all, congratulations! 5.5 is way better than 13. It seems reasonable to assume that lower is better, but that may not be the case. And perhaps more research is needed to answer your question. (Isn't that the last line of every study? "We need to further study..." Ie, we want more money.)

My favorite post on the ins and outs of fasting blood sugar and low carbing is from Peter at Hyperlipid. I strongly recommend you read the post several times and then read the comments.
http://high-fat-nutrition.blogspot.com/2008/08/physiological-insulin-resistance.html

A couple of random google hits "hba1c + mortality" cast doubt on whether getting it lower helps with not dying:
http://www.cardiologytoday.com/view.aspx?rid=64424
http://www.endocrinetoday.com/view.aspx?rid=61797

But again, the full answer is probably not yet known.

And lastly, to quote Dr. Kurt Harris quoting Dr. Doug McGuff:
'At one point in the lecture, he hints that he does not believe in doing a lot of testing. He says, “if the number is bad, eat healthy, and if the number is good, eat healthy”. What do you need the number for?'
http://www.paleonu.com/panu-weblog/2010/2/22/body-by-science-and-panu.html

Bernstein has a forum here: http://www.diabetes-book.com/

plenty of paleo ish eaters, definitely all low carb eaters.

Do you have any reason to think that your daily fasting and post prandial BG readings would give you a different average than the A1c did? Your meter's info is by far the more accurate, depending on the meter of course. Bernstein recommends the accucheck aviva.

it takes several years to develop diabetic complications. The Bernstein book has a good section on what these all are - most diabetics are not screened for all of them. He thinks that adherence to his plan - which is compatible with Paleo - can reverse them anyway. Bernstein reversed his own kidney disease with his plan.

Congratulations on getting your BG under control! I would encourage you to check your meter's info against the A1c and if you feel you need to make further improvements, cheek out the Bernstein Forum.

With you having lowered your A1C by that much, it indicates you still have some functioning Beta insulin cells coming out of your pancreas to control what blood sugar rise you may have.

Dr Davis at http://www.heartscanblog.org wants all type II diabetics to eat a meal and measure post prandial blood glucose level for two hours every 15 min to chart what food does to your blood sugar so you can see exactly how you react to food.

Truly, the best way to control diabetes is not put any more demands on your pancreas than you have to and that means going almost zero carb. Many of us eat 75% fat, 20% protein, 5% or less carbs in the form of leafy green salads with olive oil and vinegar. There is a mild insulin response from eating protein...you can test that yourself...

You asked if you can survive with A1C in the 5 range. Absolutely yes! Just know that A1C is an average glucose reading over 3 months. If you test daily glucose and your readings are 100 or below daily...then you will know you are doing all the right things.

I would refer you to this blog posting by Chris Krisser regarding A1C and why that number is less than accurate! http://chriskresser.com/blog/why-hemoglobin-a1c-is-not-a-reliable-marker/

Congrats on your progress so far. Keep it up.