Thanks everyone for your replies. It's good to know you've had success with normal sewing thread. If it was for me I would have just used what I had but when it was for someone else, who's paying, I didn't want to take the risk..lol.
I'm happy to report that my Janome (7700) is handling the thread beautifully, although I did put in the blue dot bobbin case so I had a lower bobbin tension. I probably didn't need to do that but it was there so thought I'd use it. And I'm using a topstitch needle (no 12..I think) and the machine just purrs along
