It depends on your development timeline and intended future use.
In reading your post I have the impression you are looking to the future and think the 54xx series may be better positioned for your need. Again, in the end the decision is up to you based on need, budget, development timeline, etc.
As to the FSB of 1333MHz vs. 1600MHz and power consumption issues you may require, here is a link that may help in making the decision http://www.intel.com/products/processor_number/chart/xeon5000.htm?iid=pn_det+list_xeon5000 . It shows criteria such as processor number, architecture, cache, etc.
With respect to server boards, the link http://www.intel.com/products/server/motherboard/index.htm?iid=mbd_body+sv_all#s1=Intel%AE%20Server%20Board&s2=all&s3=all may be helpful in making the decision. It shows form factor, socket, memory and processor support. You may click on the board number (left hand column) for more information about a specific board in question.
I hope this has been helpful.
Don
