The simple answer is "no, you don't need to display speed stickers". The Vienna Convention takes care of that in the respect that if a vehicle complies with plating etc in its Country of origin then unless there are any special circumstances (as in vehicle dimensions that are prohibited), it is not required to comply with individual issues. Take VED for instance. How many foreign vehicles do you see displaying valid UK VED discs? (I'll get that one in before October when you probably won't see many UK vehicles displaying either!)