though if i was gonna for sure be in a knife fight (hopefully i wopnt ever) i would carry a large fixed blade of the bowie style, my mad dog SEAL ATAK2 would be my number 1` choice, that said a fixed blade is a lot more hassle to deal with on a day to day basis vs a folder, for me anyway, and i have several bud nealys w/the MASS sheaths which are imho the top of the line in ease of carry/design of knife/design of sheath/etc, they are just more hassle, poking you in the side when ya bend certain ways, scratching/scuffing leather seats when ya sit down if ya arent carefull with the metal clip, flopping around when ya lower trousers lol, just a lot more hassle, its a lot easier to deal with a folder and i dont worry at all about the lock failing as long as its a good quality design and make, i edc either a emerson custom '13 or a spyderco Ti ATR and have exactly zero worries about lock failure on either one should the day come to pass when i need one for a knife fight, i went thru a FB phase myself thus all the nealys and polkawski's i have and have tried but i just found a folder to be fine for what i need it for, now if my primary weapon was a knife, well maybe then i would go w/a FB, maybe, i would have to think about it even at that point.
if ya do want a good edc FB the very best i have found, with well designed, functional sheaths (not all 'smiths do sheaths very well FWIW) are by bud nealy (ie the 3.5" or 5" pesh kebz, and others) or al polkawski (ie the companion and others), they are thin/lite and carry very well for a FB.
if an emerson '8 or super '8 isnt thin/lite/easy enough for you to carry i doubt ya will find a FB that ya are gonna like, any emerson folder, be it std or "super" is gonna carry better than any FB i know of, and if an '8 or super '8 is too big i dont know if ya are gonna find the spydie is that much smaller, i dont know, give it a try, i guess thats half the fun, trying different things, can get expensive though lol.