For fixed blade EDC carry, I usually max out around 3.5"ish. I carry my ESEE 3, but nothing bigger. Around my little slice of suburbia, what could necessitate a larger blade?
Even in the woods, I will only carry up to about 4.5"ish. A Mora Companion, Becker BK14, ESEE 4, etc... I just have no use for a larger blade and all it does is get in the way. That said, if i'm out in the woods, I almost always have a back pack with a small lightweight hatchet (Fiskars X7) and folding saw (Silky Pocketboy or Bahco Laplander, depending on which backpack I grab), so my chopping and wood processing needs are all taken care of without needing to involve the knife for anything other than detail work.
I do have a couple of large knives, but truth be told, they are toys to me, not for serious use. I can't think of a time where my Ontario SP5 would be a better choice than a hatchet and a ~4" fixed blade.