If Sheed can avoid a foul in the first 6 minutes (I'll settle for 1), it will be a huge boost. It will give the C's flexibility to use lineups out of choice rather than necessity. Sheed will need plenty of rest to be sharp throughout and hopefully can avoid early fouls.
Not sure if anyone has been commenting on the change in dynamics that could really mix things up (perhaps in a good way) with Sheed starting. Sheed can pull Bynum out to the perimeter, make him have to move on D, and perhaps open space in the lane for Pierce/Rondo/KG drives and rebounding. Sheed has been effective on Gasol defensively and I think can be effective on the injured Bynum. The C's 2nd unit will be small and will need energy production like they got in Game 4. If they can survive a few minutes without KG or Sheed that will go a long way to keeping them fresh for the end.
Perk will be missed -- but I think more for eating up minutes than anything in this series. The play he got injured on may have been his best box out of the series. If Bynum continues to be hobbled, Sheed and Garnett can do the job as long as their legs can stand it. Baby minutes and Scal/Shelden minutes might prove huge if they can score points and run the Lakers hard while KG and Sheed rest. Big IFs, but possible.