Yup the main problem here is not about timing difference. It's the latency. Anything from 200-400ms is definitely playable, but should it hit the 4 digit numbers you will pray that you dont become a liability to the guild. If you cant even do the T5 instances properly, going into bt/hyjal will make you a big liability to the raid seeing there are so many movements involved and if you even have a sudden spike, it would cause a death which, depending of encounters, results in a wipe. Many a fight in there require you to stay alive as the primary objective.

People in Europe have the upper hand seeing that they have low MS, not because they have faster internet connections, but because the servers are much closer to their location geographically. They typically play with a latency of between 40-150ms.