Bill and Becky Lawrence L500L would be my choice. I know you are looking for more of a Low/Mid output pup, but the L500L isn't as in your face as it's reputation implies and compared to the L500XL for that matter.
I have a mahogany SG in C# that currently has the L500XL, but I'm going to go with an L500L myself. I also have an Iommi pup on it's way, but they are a very hot pickup and prob not what youre looking for, but it's right down my alley and I'm going to throw it in there to try out for a week or so. I also have an EMG-60 that I may try in the bridge w/18v and use my rack mount 15 band EQ to dial it in a little better. My guitar is for Sabbath/Doom metal, but I might be taking a different approach to the same idea as you, so I might not be of much help, but Im trying! hahaha!
Lots of great suggestions by everyone so far Id like to add...
What is this guitar that you speak of?