So using the average between Tear's and Biffa's numbers the Intel and AMD systems have about the same cost per point over 2.5 years with $0.11/kWh electricity.
i4p Xeon
Front Price: $3500
Performance: 980 kppd
Power: 650 watts ($1700)
Points/$: 172k
OC 4p
Front Price: $1600
Performance: 700 kppd
Power: 820 watts ($2150)
Points/$: 170k
Obviously these numbers are only estimates, the better choice swings one way or the other with changing electricity or hardware costs etc.
Remember to get up to 700K+ ppd on AMD you need 16core overclocked extra spicey to 3.0+ Ghz so you are looking at around $300-450 for 62xx depending on model and $6-700 for 63xx, although you may approach the PPD of the Xeons at the extreme end of the AMD range.