Im not quite sure what stock is going to help you, but I can tell you from experience(I used to run the same optic forward), running that PA 30mm forward on a quad rail is doing yourself a huge disservice. You are putting all the weight of the Optic and rail over your extended arm, on an already slightly heavier platform. Like someone already suggested... Use the MI side mount, if you have that option, or the TWS Dogleg, and mount that CompM style sight over the receiver. This will also move the optic closer to your eye, giving you a better chance at achieving the cheek weld you desire. Ultimak sells a low-profile 30mm ring mount, its expensive, but its one of the lowest 30mm picatinny mounts. A micro is much better suited for being a forward mounted optic because it weighs very little.
If you are dead set on running it forward, and not on an ultimak gastube...... have you considered a Magpul CTR Stock with cheek riser? Im assuming "m4 traditional" is what you are after if you've already added a quad rail.