Originally Posted by Bdsm

1. MCT does not really matter if you have separate tickets.
2. HEL-ARN connection takes longer as you need to enter Finland. Also longer distance to walk in the airport, especially if HKG is gate arrival. HEL-LHR is a lot shorter even by bus arrival but especially for gate arrival. However, I only talk about hand luggage connections - if you need to collect your luggage, you need to enter Finland. Check in closes some time before departure as well, ARN connection is unlikely. LHR is later but you need to pass through passport control again.
3. No.
4. No.