Seating changes from gig to gig but C1 will be on the arena floor; I think those seats are always flat. Block 418 is presumably on the 4th level - and seats up there are - quite seriously - not reccommended for those liable to vertigo!
i have been to the o2 twice now, i was sat along the side quite far back and then i was standing, and both times i had supurb views, i think wherever you stand or sit, its a great view, i saw take that twice, best show ever, who you seeing?
i went to roger waters two weeks ago and I think the high seats would be too high - I found it quite steep where i was around the middle and when people are sitting down there is not much leg room to get out and I get a bit of vertigo and found it hard to keep my balance. I was on the side about row p in whatever block think it was about C - the view is good all round I would guess and sound excellent but would not go at the back as you wouldnt see anything as quite far from stage an the high level is very high up