My only L-N is my 60 1/2 block. My user plane is a 605 Bedrock. No, I don't think a 5 or 5 1/2 would be too big. You aren't really making the timber flat like in cabinet making, just taking the saw marks off.

My experience with scrub planes, which is a Stanley No. 40, is that they make huge furrows across the timber. Great for roughing in a scarf after chopping, but not a finish tool.