I have done both several times, but not together. The Millennium is a wondeful ship and she is heading for drydock this November to make a great ship even better. I wouldn't hesitate to sail her anywhere and would look forward to it.
Transatlantics can be lots of fun depending on the weather and how well the Atlantic cooperates. A westbound crossing is much more desireable than an eastbound because of the daily time changes.
Hope that helps.