I've never heard of a single spring 330 but I think it would be a mistake. I know when my 280s and 330s got older I noticed a significant increase in hip caught otter. That alone would keep me from using a weaker coni of any size. I know they did make 210s which were a single spring 220 but were made for muskrat I understand.
If I had a smaller opening, I would use a 280.