Two posts to the same guy in minutes has got to be a record. Answered your 3 or 4 burner post and thought you were set on a Ducane. Anyway I just bought a Weber Spirit 310 and am learning to cook on it. Its different than my last one as its elements are front to back horizontal tubes whereas my old one (Charbroil lasted about 4 years) had 3 individual ones from right to left. A great thing they don't mention about this unit is the ease of cleaning. Of course they talk about the grease pan that you can use aluminum pans in but they don't talk about the fact that the WHOLE BOTTOM of the grill slides out for cleaning. No wonder there's no flare ups. No more removing grates and working around burners to clean the drippings that got stuck. Check my post to your 3or4 burner question for other answers.

I know I've seen at least the Big Green Egg built-in. I don't think there's any difference in the grill - it can be used on a stand or built-in I believe. Here is a link that might be useful: BGE Built-In

I have the Breville. It was a gift and I was planning on returning it because I didn't need a single use appliance or to have to find a place to store it. We decided to try it. We kept it and now our son has one too. He loved it. The Breville heats very quickly, cooks quickly and evenly and cleans easily. If I were going to buy one, I would consider the one that has the changeable plates so it can be used for more. Even without that though, we've found that you can reheat a slice of pizza in a hurry and without heating the oven and other such exciting gourmet adventures. I have three Breville appliances and I don't think you can go wrong with them.

you might want to post your question in the Cooking Outdoors instead of this appliances forum http://ths.gardenweb.com/forums/bbq traffic isn't like it used to since houzz bought GardenWeb, but anyway, $6k is a tough price point, most entry level built-in is around $2k, then it jumps to over $8k. I got a Blaze 40" 5 burners built-in 2 years ago, because that was the cheapest 40" 5 burners one can buy for under $2k with a decent lifetime warranty. check it out, save yourself ~4k, price has gone up now, it was $1599 when I got it.