I think you may not need to go through security when arriving in ARN from the US.
If it is on one ticket and there are delays you should be moved to the next flight, so unless you want a leisurely transfer you might as well book the earlier flight.
Hah, well, I guess I'm now on a leisurely transfer. I didn't want to stress too much about making the transfer.
I'm still within the 24 hour cancellation period -- worth cancelling and rebooking then? Or (maybe a question for the SK boards) with *S status, can I standby on the earlier flight for free?