This is an excellent price for an long-distance mileage run, as it’s rare that I can get them close to the 4 CPM range. The Flight Deal was able to find it as low as $590, but pay a few extra dollars and you can add a connection through Houston for extra miles. Connection times aren’t bad, either. Be sure to allow yourself more time in EWR than IAH as I often find New York is where the inbound delays happen.
My suggested itinerary is a one-night trip to Oslo. I recommend you try to sleep on the plane and drink lots of coffee all day before crashing late afternoon. Or stay longer if you like. Lots of dates and lengths of stay were available in the range of $590 to the low $600s when I checked in February.
If you’d like to use a Global Premier Upgrade, include the advanced search language “/f bc=w” to limit your results to the W fare class, the minimum required for an international upgrade (remember it must also be a United-operated flight). The Flight Deal found the best price at $1,217. I think you can pump more miles out of it with a few extra dollars. The lowest price I was able to find routing through Houston was $1,221, and for $1,250 you get a lot of flexibility in your dates of travel.