What Xeon Models are recommended for my mid 2007 mac pro?

your research so far...? what are you looking at so far.

okay, someone people have read the tutorials and know their way around.

There is even firmware update for 2006 model 1,1 to make it into a 2,1 which you already have

You are looking at 53xx and there it is a matter of price and what is available but generally 5355 pair is what I would guess.

There are tutorials on how to are on MacRumors

http://www.accelerateyourmac.com or Google

Xeon "Clovertown"

http://www.bing.com/search?q=xeon+clovertown

http://en.wikipedia.org/wiki/Xeon#5300-series_.22Clovertown.22

http://en.wikipedia.org/wiki/List_of_Intel_Xeon_microprocessors#.22Clovertown.22 _.2865_nm.29

http://www.macrumors.com/2006/11/15/8-core-clovertown-mac-pro-benchmarks/

http://ark.intel.com/products/28035/Intel-Xeon-Processor-X5355-(8M-Cache-2_66-GH z-1333-MHz-FSB)

5400 are Hapertown and different socket that was used in the Early 2008.

yes, they are costly... though sometimes ebay can snag some good deals. Not a widely used server part. The 5345s are affordable but maybe not what you want to go with.

And a new system? I'd wait and save for a year. Shame when an Intel 6-core 3.3GHz is out of reach but $600 on newer socket.