from the excellent ITJungle online publication, the new Power6 p570
shows a 58% performance improvement over its Power5+ equivalent:

http://www.itjungle.com/tug/tug052407-story03.html

"...By February 2006, IBM's benchmarketeers were testing a System p5
570 server using 2.2 GHz Power5+ cores, and with AIX 5.3 and a much-
improved DB2 8.2 database, this box, with the same main memory but
only 61.8 TB of disk capacity, was able to push 1.025 million TPM for
a list price of $7.97 million; after a 43 percent discount, IBM was
able to show bang for the buck at $4.42 per TPM on the TPC-C
test. ..."

"...Jump ahead to May 2007. A System p 570 server, which has a new CPU
card, a new memory subsystem, and a new I/O subsystem plugging into
the same motherboards that the Power5+ servers used, has been tested
with the Power6 servers and 768 GB of main memory. Like the prior two
570 boxes, this one also has 16 cores, but these Power6 cores run at
4.7 GHz. This box is running a modified AIX 5.3 operating system that
knows how to speak to the Power6 chip (which is done with a patch to
the kernel) and a future release of DB2 9.1 that will not be ready
until this November 21. On the same TPC-C benchmark test, this Power6
box is able to process 1.62 million TPM ..."

"...Amazingly, the System p 570 box using the Power6 chips is set up
with not only 50 percent more memory, but 117 TB of disk capacity. The
base 16-core System p 570 server has a list price of $2.14 million not
including storage, with $1.45 million of that coming just to put all
that memory in the box. The storage IBM attached to the box cost $6.44
million, and the system software cost $539,698. With client hardware
and software and three years of maintenance, the total price tag for
the System p 570 Power6-based system under test cost just a few bucks
under $10 million. But to offset some of the cost of that storage, IBM
cut the price with a 43 percent discount again, yielding a bang for
the buck of $3.54 per TPM. That represents a 58 percent increase in
performance of the Power6 machine over the Power5+ machine, and a 20
percent improvement in bang for the buck. ..."