Most length I EDC in a fixed is 4". There are three things I'd personally be considering in an EDC fixed:
1. Legality. If the length isn't legal your other choices are moot. Why get arrested because you were packing something illegal?
2. Open/Concealed carry. Again, this is something of a legal question, since some places require open carry while others allow for concealment. This will affect the choice of sheath, and ultimately IMHO the overall comfort of carrying a fixed blade EDC.
3. Personal preference. This has more to it than just what you feel like carrying. Once the first two things are decided, and you've narrowed down what you like you have to decide how comfortable you are with carrying the knife EDC. 9"+ is a lot to have shoved IWB. You also have to consider the "Dundee effect." This is where NKP's (Non Knife People) reactions to your knife will change based on the size of your EDC. with something over 9" you're likely to cause a panic if you pull it out to use it in any urban setting. Even if the knife is legal and you can carry it concealed, when you pull it out that just makes the reaction worse because they weren't prepared for you having ANY knife let alone a large fixed blade. Now, am I or any other knife person upset by this? No. However, we live in a society where the personal carry knife has been nearly relegated to a purely convenience item. Given that, people aren't as used to seeing a knife used outside of the kitchen. Now, I mention all of this because if you're at all concerned about the reactions of others you may be hesitant to use that fixed blade you carry for EDC and might use a smaller folder instead. Well, if you're using a folder instead of that 9"+ fixed blade for your every day cutting needs, why would you want to lug all that weight around with you? Even if you decide you want to carry it, and use it, you still have to be prepared for the occasional bad reaction. Some do-gooder is also likely to call the police at some point, so keep that in mind. If you're legal, no big deal, just nicely explain yourself to the officer who shows up. Be polite, though, as there are quite a few police officers who are not quite up to speed on exactly what the laws are regarding knives; and they're responding to a call where someone has been reported to have a large knife while acting suspiciously. They're used to dealing with felons, so you may have to be patient while they change gears. If you're overly upset they may not make the transition from "guy with knife reported by aggitated citizen" to "guy mistaken for someone suspicious by a citizen who has no idea what the law is."
I'm not trying to preach at you, just giving an honest opinion.
ETA: Personally I say if you like it, find it comfortable to carry, and its legal who cares what NKPs think about it? Just be prepared for the fact that some of them might not like it. Then again, your freedom and rights are NOT dependent upon their comfort.