The John Graves you cited in Co. B, 4th Arkansas Cavalry (CSA), is John J. Graves (born c1843 in Mississippi). He resided in Conway County, Arkansas.
The William Graves you cited in Co. I, 4th Arkansas Cavalry (CSA), is William G. Graves (born c1838 in Blount County, Tennessee). He subsequently served in Co. I, 2nd Arkansas Infantry, U.S. Volunteers. He is believed to be a resident of Scott County, Arkansas (unconfirmed).
In tracking down ancestors who served in the Confederate army, you should concentrate on units organized near where they lived -- at least in the same county or neighboring county.