I'm currently playing as the king of Eire in Charlemagne and I am around 150 years in. I've started to expand into England and will soon hold all the southern counties. With the bonus of the additional holdings I was considering changing my capital from Dublin to Middlesex and my duchies to Essex and Kent.
The only downside I can see is my technology in Dublin (e.g., legalism etc.) is currently higher than in Middlesex. Will the technology transfer or will I lose it and adopt the technology levels that Middlesex currently has?
Are there any other disadvantages to moving my capital that I've not considered?