cwave,
About 12" to be exact... /w3tcompact/icons/wink.gif Sorry, I just couldn't resist!! /w3tcompact/icons/laugh.gif
There have been many discussions revolving around MMM deck size vs the application. That is what it boils down to. Do you have a lot of curved areas or a lot of straight mowing? If you have mostly straight areas to mow, go for the bigger deck. If you have a lot of trees or curved flower beds, etc, you may wish to go with the smaller unit for manueverability.
As far as the ballast implement, I have never seen or heard of it before. I do not know if it is a JD implement or an aftermarket implement. Looks like a neat concept. However, there are differing approaches to solving the problem. One is to buy a JD ballast box (my preference). It is cheaper in the long run. The ballast bar cost $239. If you buy 42lb suitcase weights, they're approximately $34 apiece. The bar holds six of them. It would cost you nearly $450 to have about 260lbs of ballast. If you use the ballast box, it costs about $150 and you can add 6 80lb bags of quick-rete. The box weights 88lbs giving you 560lbs of ballast. The cost of the quick-rete is about $5 a bag - $180 total investment. I'd go that route and take the $270 and apply it to other toys, errr, implements. /w3tcompact/icons/wink.gif
There are other methodologies - rear blades (grading or box blade), wheel weights, filling the tires with liquids, constucting your own ballast box. As far as towing, you can buy a Cat 1 drawbar and a towing ball for about $30-35 to move small trailers or just put a ball onto your drawbar under your rear PTO.
Terry