It reads F2A55-M/M11BB/DP_MB Asus. Want to upgrade processor has A10 6800k right now with 750 Ti. So I'm not sure if FM2 or FM2+. And which would be best processor to replace tia
There won't be any real difference between the ones you listed and the A10 6800K... if you really want an upgrade go with a ryzen chip.
My 6800k is 3 yrs old, so just want to squeeze another year or so out of this PC, and looking only to spend 100 bucks the ryzen too much rn but
AMD Socket FM2 searching for best CPU usage for rn
As I said you won't get any real performance increase going with an athlon x4... it's a total waste of money.
Aso the Athlon X4 860k/870K/880K require a FM2+ socket and your motherboard has a FM2 socket, so these CPUs won't even be compatible.
It's clearly stated in the compatibility list of your motherboard posted above the the X4 760K is the best athlon you can upgrade to and that won't do better than the a10 6800k you currently have.