That can only work in larger schools.
As I said up thread, my comprehensive was fairly small and the top set ended up with kids that shouldn't have been in the class - but the school couldn't really have a bottom set containing 35 kids and a top set containing 25 kids.
The only way that a comprehensive could allow the brightest children to move at the pace of a grammar would be to have massive schools with multiple sets - e.g. elite, top1, top2, upper1, upper2, upper3, middle1, middle 2, middle3, middle4, middle5, middle 6, lower1, lower2, lower3, bottom1, bottom2, leaning disabilities1.
That would be at least 18 classes per year group in an attempt to accommodate the normal distribution of abilities and just isn't realistic anywhere but the inner cities.
A separate 'elite school' covering a large rural area is the only practical solution.