I understand that using threshold etc in PS can get the highlight needed. I think it's a better option to tell maya to render the original image AND the specular out as different passes in the same render to different files. That way you get exact control on the specular... Though... I can see the point of using the threshold as you can adjust the size of your man made specular channel (layer).

Thanks for all your help... It's got me headed in the right direction...