How do different length drives affect performance? I'm looking at a 40" but I'm not sure that is the best fit for me. I live up north and break ice, run mostly marshes and a few river.

We run a 40" on our MB7000. Having the prop further away from transom seems to give it better bite. Running in less aerated water. We coverted a couple older MB hypers to the longer 48" shaft and found them to run a couple MPH faster than the short shafts. Only thing is they won't turn boat as tight when running flooded timber. We run mostly shallow sandy bottom rivers, and found they run well in Ice also, gets prop down under ice where it gets better bite.