Don't limit yourself to 6 boxes. Yes, I know shipping more will cost more, but it will get REALLY stressful if you sit there and keep reminding yourself that you're only doing 6.
My 6 boxes turned into 9 (so far) - and they are 9 boxes filled with family herilooms, antiques, sentimental stuff, and scrapbooks/scrapbooking supplies. I even went back through my first 4 boxes and I only managed to take out 5 books - that's how thoroughly I had gone through things the first time!
I agree with Mops - make yourself piles (or bins - that's what I did). Talk on the phone to Kevin (am I right? Hubs is Kevin?) while you work on it. When I was going through my books, I found it helped to have Tim on the phone because I found out he already had some of the books I wanted to pack, or knew a used book shop that catered to the interest for replacing books.
Remember that you don't need to justify everything you take. If you want it, take it. It's been driving me CRAZY that I have some family members wh think I'm taking "too much". Hello? MOVING HOUSE. At least I don't have any furniture I want to move!