The answer to the question is No, you will not need to do the JAA performance exam.
The rating that you will need is the CessnaSET Class Rating
(see here). Since the 208 is not designated as HPA, there are no pre-requisites for the training which, being non-approved, can be as much or as little as you need to reach the required standard for the skill test and can be done by any suitably qualified FI or CRI and without the need for an approved training organisation. I'm not aware that the figure of 4900kg has any relevance in the JAA.