casting inline spinners

I have been making my own in-spinners for a while and I guess finally this year I realized the larger ones are to big for the rods I have. My brass bodies are 1/8 oz and i put either a # 2 or # 4 french spinner on them, most of my rods are light/medium action rods and they have no problem chucking the spiners with # 2 blades. Problem comes with the # 4 blades; they just seems like they are putting a lot of stress on the rod. I primarily fish the bad river for northerns and the shiawassee river between Corunna and Chesaning for small mouth and everything in between. I know i need a heavier action rod but i don't know how much bigger I should go with out going to big, like a M or M/H rod? Thinking it would also give me a excuse to get bait caster. regardless of what type of real that is purchased what would be the preferred gear ratio for casting in line spinners or does it not matter?

casting inline spinners