The problem with this scenario is Ferris and Heaslip are free to make hay. Which is not an ideal scenario. I don't believe Wales can afford to manmark any of the Irish backrow.
Not really, because Faletau and Warburton are excellent defenders aswell. Faletau in particular is great around the fringes, while Warburton is often the man leading the defensive charge. O'Brien is a great player, and he needs to be kept quiet, I think Lydiate is just the man to do this (Kaino aswell if the two meet).
Re Wales targeting the O'Gara channel (if he's starting)...Ireland and Munster are well used to teams targeting this...and it is said before every match O'Gara is starting. Its rarely you see teams gaining a huge advantage by doing this...yes i know he can get run-over from time to time but the majority of the time this channel is defended very well by the team, when you consider it is constantly targeted. Also Ireland have one of the best defenses in the world. i think i heard somewhere that they havnt conceded a first half try all year in a competitive match.
Maybe Ireland and Muster are used to teams targetting this, but it doesn't change the fact that they've got someone in a pivitol position who can be stemrolled by Shane Williams (I know it was a while ago, but still...). By having to cover somebode else, there could and should be gaps elsewhere, it's all good in my mind, whether or not the breaks are actually made down ROG's channel.
As for defense, I agree that Irlenads defense has been impressive. But another stat to throw out there. It was mentioned on ScrumV last week that Wales hadn't conceded a single linebreak in this world cup (although I'd personally consider Hougaards try as a linebreak), and I don't recall Fiji making one today, now that is pretty darn impressive!!!
Edit. Wales will have a fully fit squad to choose from for the QF clash with Ireland.
http://news.bbc.co.uk/sport1/hi/rugby_union/welsh/15145079.stm
Really didn't expact that to be the case after three hugely physical encounters against SA, Samoa and Fiji! I know Hook, Shane and Lydiate will be short a week or two, but I'm over the moon by that, I was expecting to have half the squad injured by the end of the pool stages tbh. I think that's probably another sign of the fitness of the players, I've always belived that fit players are less injury prone (although freak accidents, such as broken bones can strike at any time).