any point continuing expedition after 7 wins on 1st run?

or is it more efficient to retire & claim so you can get into a fresh run quicker..?

rewards are capped at 7 wins right, so even if you go 7 wins again in 2nd run, you don't get any extra rewards..?

Your rewards won't improve after getting 7 wins on your first trial, but you will still gain the bonus experience corresponding to the wins you get in your second trial. It's up to you to decide whether that's worth it or not. Personally I always try some weird stuff in my second trial if I got 7 wins in my first, because getting 7 wins when it doesn't matter kinda sucks. This way I still get some nice extra experience but I also don't have to worry about performing well.