In the scheme of things, as you say, your diagnosis is very good. But if I were in your situation I'd also be concerned by the advice you've been offered...I've just done some Googling and found articles from eminent institutions that back up the "over 3 cms" cut-off.
I also found a recent article:
https://pancreasfoundation.org/wp-conte ... NCREAS.pdf
"Patients with branch duct IPMNs who are symptomatic should be treated with resection not only to alleviate the symptoms, but also because of a higher likelihood of malignancy. It is important to emphasize that the decision to treat should be individualized and based on patient preferences and willingness or unwillingness to undergo follow-up studies, as well as on the availability of safe pancreatic resection."
So the fact that you are symptomatic is also something to take into account.
During the 2.5 years that hubby and I have been on Planet PC we've sought second opinions several times and never regretted it. This is what we would do in this situation. Also we would speak to the wonderful nurses on the PCUK Support Line.
But I hope you can derive a lot of comfort from the fact that there's a good chance that your ipmn is benign, and that if it isn't, it's very treatable.