As far as support and drivers go, I'd be tempted to stick with 3ware
because they've been doing RAID 5 ATA the longest and ATA controllers the
longest. Drivers and support to me would be more important than a
fractional difference in speed in a server situation.
As far as speed comparisons, there aren't really a lot of good ones. Most
speed tests I've seen compare 3 or 4 drives max, and 7200rpm ATA to 10k or
15K scsi drives isn't exactly a fair comparison either. Obviously there
are speed advantages to modern SCSI server drives and there is a price
premium associated with that, which is what you aren't paying for in the
ATA drives.
If you really want high-end ATA RAID 5 you can get pre-packaged arrays from
Promise, Adaptec, and even 3ware. Adaptec just purchased Qlogic which was
making high-end ATA arrays for the near-line storage market. Even EMC is
coming out with ATA solutions for near-line storage. These solutions have
very smart caching and striping with very big battery backed up caches (up
to several GB) and would be the fastest and most expensive performers of
ATA storage solutions. But they are also the most comprehensive offering
true SAN type abilities like 2 or 4 Gb/s switched fabric to multiple
servers or direct scsi connections to single servers.
