Just back from my ARN-ORD-LAS trip where I got my optiontown upgrades to C both ways on the TATL leg. Really glad I had the C ticket on the way from ARN, since I picked the time when every swede was leaving on vacation. ARN was a madhouse with long lines even for EBG and F checkin and the fast track access was nice. Can't say the lounge in ARN is worth it, especially being a hike from the F-pier.
UA let me check in at the business counter in Vegas, unfortunately I didn't get priority tags (turned out I didn't need them, bags came off first anyway) or security fast track. I had forgotten about the suck that ORD T5 is, with no fast track or food airside but the lounge was OK.
For 3kkr extra it was worth it to have a seat I could sleep in and not have to deal with lines at ARN.