This is brilliant info John, thank you so much. Could you clarify what you mean by
"Think about a) sending small amounts of traffic to your new pages to track conversions and interaction and b) you can expose some specific pages to the search engines to see how the search engines treat them. This would be very hard to do with a separate site." ?
Are you suggesting rolling out the new site page by page would be better than all at once? That wouldn't be possible if rolling out the site on the current domain... It would be great to get a proper handle on exactly what you mean.
Thanks for the contact info- I will be in touch!