From another thread, the increase in possible transistor count vs the number probably needed for 8 more pipes probably doesn't add up.
Then again, you can't be sure how many transistors will be needed for 8 pipes, or exactly how many transistors are on the die, or exactly how the the die is.
It's basically all speculation as to what could be true, but from the numbers given, 8 more pipes seems a stretch given the die size/transistor count.
One thing that is bugging me though, is the fact that everyone's saying 32 pipe card.
What's to stop a 28-pipe car being made (it's one extra quad), unless you need an even number of quads (but that doesn't work since the X800Pro and 6800 have 3x4), so if they did have a few more pipes up their sleeve, why not 28? It wouldn't be a huge leap, or they could release a 32, 28 and 24 pipe set of cards.