One nice thing about seeing a thread like this, late in the process is, I got to read the start.....and got caught up to the end pretty quickly!!
I've burned stumps like that before (though typically smaller) and I've learned that 'for me', a stump like that would probably take three fires to completely get rid of it. I don't do anything special, just pile things up in a wide space and light it.
I personally would burn it.....well....because I enjoy burning things!! I'd not want to bury it and have it possibly create a depression later on or, maybe become a hideout for yellow jackets (I had a stump do that once and I got nine stings on my face)
Either way, keep plugging at it, job well done!!