Looking to move from Ex2K to Ex2K3 on new hardware.

I currently have over 1000 mailboxes on Ex2K, database currently around 45GB
in one storage group, another 5GB in public folders. OS = RAID 1, DB + Logs
= RAID 5 (5 x 10Ks). Originally the 5 disks were setup as 2 for Logs and 3
for DB, but as the DB grew there was no choice but to increase the RAID 5 to
5 disks as funding wasn't available. I mention this as the server runs
poorly when our users decide to send 25MB+ emails around.

To improve performance and allow for growth I am proposing the following :-

Dell 2850 - 2 x 3G XEON, 4G RAM
OS = 2 x 36G 15K (RAID 1)
LOGS = 2 x 36G 15K (RAID 1) (Logs are currently only a few GB per day)

PowerVault
DB = 9 x 72G 15K (RAID 0+1) (9th disk as standby)

The MS documentation seems to steer away from RAID 5 due to write penalties
(eg below link)

http://www.microsoft.com/technet/prodtechnol/exchange/guides/StoragePerformance/
049faa66-321e-433f-8df8-083e52e7ae5e.mspx

I've also had a look at HPs sizing tool.

As part of the migration I intend to introduce at least a second storage
group keep each one below 30GB.

Interested in anyones views on the suitability of this new hardware. One
area I'm yet to finalise is the controllers and channels. I'm assuming that
I can use two channels on the internal controller on the 2850, one for OS
disks, two for Log disks), and I can install an additional PERC controller
for the RAID 0+1 array. For the 0+1 array should all the 9 disks be one one
channel, or should each side of the mirror be on its own channel ?

Thanks for your time.