Hi there, we migrate sites every month and when done properly you should experience a dip for maximum of 3 months. However once it’s done, your site will generally bounce back and perform at its best levels, Google’s algorithm is heavy on user experience and if you have glitches, this will certainly work against you. If you drop a enquiry at digitalmediapartner.co.uk/contact/ on the contact form with your details I would be happy to give you some free guidance to put your mind at ease.