When to move on?

Patch 3.3.2 hit the servers today, and that means Arthas can finally be defeated. All across the world, guild after guild is pushing their way through the citidel to match up against the villianous Lich King and find glory in his final defeat.
Not my guild however. My guild is still ironing out the wrinkles in our raid team. While I show up to main tank every raid, the offtank position is constantly rotating, as well as some healer and DPS positions. We are still learning to work together as a unit and progress through content we haven't yet defeated. All of this means, we are still fighting through Trial of the Crusader. And, no, we haven't successfullly completed it yet.
I admit ICC scares me. We have enough gear for the content, thanks to the Dungeon Finder and Emblem system. We have people who will get nothing from ToC but progression and experience, which is exactly why I am adamant about staying where we are and learning to defeat ToC before we take on ICC. And therein lies the problem.
I've seen many a player jump ship and move on to a guild that was further along progression-wise. They get frustrated and bored with being defeated by the same content week after week. They know they're ready for more and they begin to feel held back by those around them.

As a guildleader, I need to be able to recognize this issue and force a jump in content when it's time. The only problem with that is if the team fails in the earlier content, how successful will they be in the most current content? We made jumps in the past, not quite finishing Naxx before jumping into Ulduar. Not finishing Ulduar before moving into ToC. But now with only five boss fights and no trash, I feel like this needs to be done before moving on.

I know I could be wrong in that assessment and I may have to move into ICC before we finish ToC just to keep people satisfied with their chosen guild. But failure in ICC could then be seen as a sign that this guild cannot complete the content. And that leads to the mist dedicated raiders looking for more dedicated guilds. That hurts the raid team and the guild as a whole. No one is leaving yet. No one has expressed a desire to leave. But Ive been in this position before and people get impatient when they see others successful while they are failing, and can anyone really blame them for looking to better their game experience?

With Arthas now in the game, other guilds will defeat him. The timer is now ticking. Either we get it done now or we have to move onto ICC.