Look at the last post by tiro_uspsss
I can confirm that my E5640 works with my Asus X58 Sabertooth
That's the Xeon you have right?
Your Xeon is pretty much a I7 920 dude. Try it and if it doesn't work just send the board back (it's Ebay afterall so Paypal have your back).
The Sabertooth was among the very best X58 boards ever tbh. It helped that it was a very late to be released board so Asus pretty much knew what needed sorting out and what didn't.
Edit. Sorry, just saw Jame's post and realised you have a X5550
Let me do some digging for you
Edit. Yes it works..
http://www.hardwareluxx.de/community/f248/problem-sabertooth-x58-und-24gb-ram-843441.html
Translated to -
Hi, I'm now due to the low prices of RAM for my little server / workstation / test station upgrade from 6GB to 24GB indulgence. . Unfortunately, with small obstacles
CPU is an Intel Xeon X5550, OS Windows 7 Pro 64-bit. Edit: ASUS Sabertooth X58 mobo with BIOS 1304. was by far 3x2GB Corsair CMX6GX3M3A1333C9 installed. upgrade now I wanted to 6x Kingston KVR1333D3N9/4G. The Kingston are loud QVL (but here with Samsung and not ELPIDA like mine) compatible with full configuration. MY PROBLEM: The RAM modules are fully recognized by the BIOS, and disable the QUICK BOOT. Unfortunately, I just come to the "Starting Windows" and after 1sec Gibts NEN REBOOT. If I plug only 3 modules (12GB) in the beiges slots it will boot, but I'll put 3 modules in the brown nothing works, fan drive on full throttle and no POST ... Unfortunately, Windows has not written anything in the event viewer, and I zz. no free disk to test it with a new installation with Win7, Win2k8 R2 or ESXi. Any ideas? Would be extremely grateful for any help any tip.
So there you have it. Board confirmed working with X5550 and 6gb Corsair ram.
The only thing you need dude is
1.65v ram DON'T use 1.5v as the board will be unstable. You need ram that can take 1.65v to run at 1600mhz.