My DS entered the Pre-IB Middle School Program, which prepares him for the IB program in High School, last year. (6th grade) He is also identified as Gifted.
He was an A+ Student in Elementary School and was in the "gifted" program there, which in my opinion was crap... it was a 1/2 a day pull out once a week...
He excelled last year in the MS IB program finishing 6th grade with straight A's.
As I understand it the IB program in Middle School is designed to prepare them for the actual IB program in HS.
My son was challenged and had a lot of homework and I think he learned a lot, but he wasn't "overworked" and was still able to participate in Band and other activities.
All of the Middle Schools in our district offer the Pre-IB program and I would say that there really isn't a "Bad" Middle School... DS is attending the school we are zoned for where all his friends in the neighborhood attend.
Overall, I'm extremely happy with the program. I would recommend the program to anyone whose child was intelligent and motivated. I highly recommend that you and your kids develop good organizational skills (if you don't already have them) in order to manage the amount of work.