M1 Single Plane Question

Heres the traditional method for setting shooter size. Snap the throttle wide open from a flat idle with no load. Keep going up in shooter till theres instant throttle response, then test drive the car. The right size is usually a size or two bigger than the one that works with no load. Might be 3-4 sizes bigger if the car is heavy or doesnt have enough converter. Its possible you may not have even needed the bigger pump, but it doesnt hurt to have it. If you can get the 950 to respond crisply off the starting line, which you should be able to do with tuning, it should out-perform the 750. I dont know much about your combination, so its POSSIBLE ( but not likely, unless its REALLY mild) that it doesnt need any more than 750 cfm. Smaller carbs are more forgiving of shoddy tuning, as the smaller venturi size will increase booster signal, so the car will pull fuel through the booster sooner.