I have a 2.26 Nehalem MP right next to me when I type this and besides a very slight hum from the 2 large fans it is silent. I have no old version to compare it with but my machine is IMO very quiet. Sofar I find it is doing what it is supposed to do without me having to wait for it which for me is the most important part.
Now I have to find some affordable 4Gb sticks (or wait for them to come down somewhat in price) and get 3 large drives (I have decided to stripe 3 drives and do backup external to save me the hassle of going the Raid5 route).
I have the same machine. Here are the XBench drive speeds. I have with a 3 disk RAID0 each with 2 partitions , the boot drive and a FW800Drobo.
Xbench Version 1.3
System Version 10.5.6 (9G3553)
Physical RAM 8192 MB
Drive Number 1 2 3 4
Uncached Write [4K blocks 96.00 320.56 310.49 35.73
Uncached Write [256K blocks] 82.78 274.17 273.70 31.73
Uncached Read [4K blocks] 28.45 23.49 24.17 2.73
Uncached Read [256K blocks] 91.35 290.33 270.67 44.64
Uncached Write [4K blocks] 2.01 10.94 10.78 2.39
Uncached Write [256K blocks] 73.31 239.83 289.38 9.47
Uncached Read [4K blocks] 0.67 2.00 2.15 0.40
Uncached Read [256K blocks] 29.03 54.19 58.44 9.73
Drive 1 = WD Caviar Blue 640 Mb WDC WD6400AAKS
Drive 2 = WD RE3 WDC WD1002FBYS 1 Tb - 3 Drive RAID0 40 GB Inner (Fast) Partition
Drive 3 = WD RE3 WDC WD1002FBYS 1 Tb - 3 Drive RAID0 960 GB Outer Partition
Drive 4 = Drobo 800 FW with 3 1 Tb Deskstar 7K1000.B 1TB Drives
(Using Code was the only way I could get the columns to line up as the formatting removes spaces otherwise)
Interestingly, the small speedy outer partition is not any faster than the rest of the 3 Drive RAID0.
The RAID0 is significantly faster than the solo boot drive.