clva2010 :
This is kind-of my current specialty. Forget about what these folks with an agenda are offering you. These yahoo's are telling you what they like or need and not answering what is best or what your heart desires. I've been exactly in your predicament. The 5800K was mine & still is one of my PC builds. Have you seen the new 7th Gen APU's? I'm not sure if they'll fit in the FM2+ but it wouldn't make much sense for no compatibility. An 880K with a GTX 950 works quite beautifully. Get yourself some 2400mhz memory as it works great with those APU's. The 7870K is a pretty capable little unit too. I've got a 7700K with all the trimmings sitting in the other room to be assembled. Lazy streak right now. Anyway, there's nothing wrong with your PC. I've got an Intel 6700K system that's supposed to be my personal rig but I have the most fun w/ the AMD stuff. You can also go with the FX line but a new MB will be in your future. Faster memory(top-it-out),beefy PSU, GTX 950 & an SSD(850 EVO) if you can swing the cost. You'll have a new PC that brings smiles. I'm guessing this is kind-of what "you" want or need? Hope this helps.
You need to read what I said more closely, if you think I have an 'agenda' (I'm the only 'folks' or 'yahoo' responding.)
The OP asked for a FM2+ Upgrade to the A10-7700K.
I said that the 880K was as good as it gets, but also said that it was not cost effective. You said that the 880K works well and you have a 7700K that works well and there's nothing wrong with the OP's system. Sounds like you agree with me that there's no point in upgrading.
The 7th Gen APU was announced the day AFTER I posted, is not currently available, and may not be so for many months, and requires a FM4 motherboard and may use DDR4 memory, so it's not an answer to the question, and it is part of the new Zen series (actually Bristol for the APU, I think), I mentioned myself.
Today, there is no cost effective FM2+ upgrade and there is never likely to be one.
Today, that leaves only Intel as a choice for an upgrade and that requires a complete system rebuild.
'Tomorrow' when AMD has released ZEN (in the sense that you can actually buy it and we know its needs and characteristics) ZEN FX and the similar APUs might be a choice, although I would never generally recommend and APU to anyone who plans to use a discrete GPU. That will also require a complete system rebuild.
Today, plan B, is to overclock, something else we both suggested.