As far as I was aware, the middle pickup is basically just a neck version anyway that is wound a shade hotter. Tonally, I think any difference is down to pickup positioning and height adjustment more than anything else. The single coils I use are bridge versions put in the neck and middle positions. The middle pickup is wound just 0.5 more than the neck and its tonal difference is primarily driven by the fact that I have it further away from the strings so it doesn't interfere with my pick.