CTF is based on teamplay and you can't really believe that coordinating a team of 4 players is harder than a team of 5 players.
Ironworks might not be perfect for 5v5, but c2 and w2 are really no 4v4 maps at all and were played in 5v5 for almost 10 years now.
People just seem to think that aim is the one and only skill in quake, while playing CTF is so much more than just aim.
People just seem to forget more and more how to play ctf and think that with aim they are going to succeed, but think about players like ooze, who made brilliant flagruns .. would that have been the same with only 4 enemies?
Wow I really don't have enough spare time to reply to all your 'arguments' and it's not that important to me either, but you really put some effort into that.
All i can say is that personally I just like 5v5 more and I don't agree that all your arguments really speak pro 4v4!