SBS 2008: RAID 5 -> RAID 1 migration bare metal restore

Ok, to speed up an aging SBS 2008 Dell Server with a Perc 6i card and give the data a bit more breathing room, I'm 'upgrading' the drives from a 3xRAID5 configuration to a 2xRAID1 configuration. The drives are configured into an OS partition and a data partition.

The biggest problem is that the OS partition is really full. I've moved all the major services to the data partition but it's still a constant battle to recover space on the OS partition so it time to put everything on a bigger set of drives.

I was planning to simply do a bare metal restore using Windows backup but I'm unclear if I can configure the partition sizes beforehand (or during) the recovery. I really do not want to do the restore, only to find out I can't change the OS partition size.

Failing that, any inexpensive cloning software out there that's Perc6 ready or other partition management software that's happy messing with PERC6i RAID1 or RAID5 drives?

I'd rather not spend £250+ on a server version of disk management software if I can make do with a standard £40 version. It's a one-hit project and there's no need for the server to be online for any point in the migration.