Hard to say of Kode or Quad would be better, but since B&J seems to be what you're gonna use the board for the Kode to me sounds like the best choice. But something to remember is that the Quad 76 is a very big 76 liter board (58cm wide) while the Kode 74 is a rather small 74 liter board. In fact, I would even say the Quad76 sails bigger than the Kode 80.
Everything depends a bit on your weight, but if you are not really light, I would suggest that you go for the Kode 80 which will handle 5.5, work perfectly with 4.7 and handle 4.2 well too. And it will leave less of a gap up to the Kode 103 too.
But if you're intrigued by the Quad 76 why not have a go. I haven't tried it in single fin mode myself (I have a convertible but just like it too much in the quad setup). But many reports say it is indeed really good as a single fin. The Q76 handles 5.5 well and 4.7 too. 4.2 can be a bit hectic at my weight (72) but especially in for B&J sailing (as opposed to full on wave sailing) its perfectly manageable.