Hi Andy,
Thanks for the feedback - this is the response I was after. I was/am pretty wary of a total change to a CMS due to SERPS and was aware of the possible affects of even a template change. I will be updating the template site-wide, but am happy to take it in stages. I will be updating portions and add new pages on a slow roll out.
I also realised that a change to a template would affect the google cache page - so that while the url didnt change - the content and structure will as far as it goes so it would "reindex" that page. Hmm - the reassement of the site following major changes I had not considered - thanks for the heads up.
Appreciate your thoughts
Regards