Late Q4 to Early Q1 '08.
While the CPUs will be a small step up, they will not be a revolutionary change. That will be closer to Q4 '08.
The Penryn's will gain a small percentage per cycle and run a little cooler and perhaps OC a little better.
The bigger up coming change is perhaps the new NVIDIA cards in November. There are lots of rumors ranging from a minor update to a new monster being released.
Since the new card will support PCI-E II and that support will be seen with the soon to be released P38 chipset, you may want to wait until that is released. Then you may start seeing more leaks on the NVIDIA stuff.
Zen, there is no such thing as a P38. You must be thinking of the X38 chipset.