My company used a X4500 and we discovered the bug that caused Sun to make the X4540 - the Marvell SATA chipset in the X4500 had a serious bug in firmware that was exacerbated by the Solaris X86 Marvell chipset driver.
Under heavy small block random IO intermingled with heavy sequential large block IO, the box would kernel panic and hang - only a power cycle would reset the box.
Sun ended up refunding us the cost of the servers and providing us exceptionally large incentives to purchase Sun StorageTek storage.
It wouldn't surprise me if the X4540 would have similar issues because they were rushing to replace the X4500 to try and minimize the possibility about bad PR over the X4500 being amazingly unstable.
This is why I'll be waiting for FreeBSD to support this because they will probably have better SATA chipset drivers and the chances of the system hanging because the Solaris kernel drivers for the SATA chipset (nevermind that it's a SATA chipset that Sun put into their own board).