Well firstof let me point out that you will not like the answer.
Specular map just imples one faxct it affect sthe specular cahannel if there happens to be one! Offoucre since the spechular channel is affected by many different channels you coyuld say that ALL of theese would be specular maps. So wichever you choose depends on the effect you want.
Yes blin model is different form the specular highlight of phong for example and yes you can do as much as you like to thei end in your delujx shader. HELL you can even use shadingmodell to color and make the blinn totaly balck and directly use teh spaculars of it form the delux allready. (altough by reading the slimtemplate for Binn and convertting its specular componet to delux isnt hard inst hard its just copypaste realy).
Second you do offcourse understand that in reqality theres no such thing as specularity! its just a crude guess besed on early optimizations so whatever WORKS for you is teh right way to go. Altough certainly in practuice having one or 2 different specular modeslls to slap on newer hurt anybody.
So in the end you choose the channel that happens to do whatever effect your after. Roughness i sone good choise as is ano of the ooethers. BEst texturetrs tend to map them ALL.
Theres a school f tought that maps the color since specular is additiive so it has most impact. Personaly i amp them all.