C.B.
I have no experience with the Summit XC double. We have the BOB duallie and absolutely love it! We actually refer to the stroller by name, "Bob" and consider it one of the family :) We bought it when my oldest was 3 and my youngest had just turned 2. They are now, 5 1/2 and 4 and both still fit in the stroller fine. My girls are very tall! I love the separate sunshades because they never both want the shade down at the same time ;) We now have a third and it's still wonderful... baby and youngest sit in seats and my oldest loves to sit in the footrest area - there's plenty of space for her there. While on trips, we've actually fit 4 children in it with no problems and it's still easy to push. 2 in the seats and 2 in the footrest area. My only complaint is that we didn't buy it sooner. Good luck with your decision :)