I could only find a comparisson with core 2's when I searched - let me know which thread if you know one. The xeons are interesting because of the possiblity of multi processor mobo's.
Now, I can see from published benchmarks that the i7 is great for gamers, and obviously thats intel's target market, but for generic tasks, like photoshop etc. etc. which are more computational, it seems that the i7's are not that impressive in the benchmarks against core 2's being only 10% faster which is a lot of $$ for a small improvement
Whats not clear to me is why a 4 core processor can outperform 8 cores in 2x xeons. We've seen HT before, and it never impressed me. In my applications (electronics simulation etc.) each thread is flat out, computationally, so the core is occupied completely, so I dont see how HT is going to help. Maybe there is some subtelty I dont understand?
That's because Nehalem (Core i7) features Hyperthreading, which converts one core into two threads - 1 physical, and 1 logical. Hyperthreading simply takes the unused portion of the core, and spin off a logical core off it. Therefore OS actually detects the CPU as 8 "cores". So in essence, it was an 8 thread machine vs. an 8 thread machine.
As for comparing between Core i7 and Core 2s, it really depends on the programs you are going to run. If you're going to run games, chances are you won't see a big improvement. However if you run CPU-intensive applications such as AutoCAD, or rendering programs, you'll see a significant improvement.
Now, if you're really considering multi-socket computers, then you should really take a look at Gainstown - Core i7's server part.
See an improvement in which? i7 or xeon? for autocad applications? I am trying to figure out which to buy...
In the end we actually bought a dual processor Xeon machine. This gives me 8 cores. I can't compare an I7 directly, since I dont have one, but I can report that in the same cad simulation the dual Xeon was 7.5x faster than a core 2 duo of the same clock speed and FSB - Pretty impressive!
To be clear - the speed improvement was way above just the number of cores. This has to be due to the fact that Xeons have a more efficient memory interface better suited to multiple processors.
The total memory on each machine was the same (the 2x Xeon board looks a bit bare :-) ).
Comparing the price of this machine with an I7, we would have spent an extra $500 for probably worse performance with the I7. In fact the machine was a snip for <£1500 (UKP).
Of course I now get asked to do seven times as much work
I have the 2 machines, a Dual Quad XEON X5355 2,66Mhz - 16 Gb FBDIM RAM and Core i7 950, 3,1 Mhz and 12 Gb DDR3 RAM. The Xeon is faster and can run multiple applications better. Vegas 9.0 64 rendering on Xeons beats the i7 visibily. The only problem is when I use apps that uses mainly 1 core, in this case, the Xeon is slower because of the clock, like Super PI.