I agree with M.Mouse and ASRAAM. I think any discomfort is due to the performance of the aircraft as opposed to the air-conditioning system.
We did an 8 hour flight recently and we went straight up to FL390 for the entire cruise, furthermore, we could have climbed even higher than that towards the end of the flight ie. FL410.
The B777 achieves a higher initial cruise altitude than the B747 which results in prolonged exposure to a high cabin altitude. Whenever, I've been above FL400 the cabin crew have generally noticed it before we've said anything to them. This usually occurs towards the end of the flight when they're busy with the final meal service. The complaint is usually shortness of breath.
I don't suffer from nose-bleeds, dryness or shortness of breath. However, I'm concerned about the more hidden effects such as increased exposure to radiation when flying above FL380.