Hi!
First of all, I would use SME 6.01 with our update script. (see my sig) 6.0 is still Mitel based, 6.01 has some updates and is already Community based.
If you can wait several months, you could wait for the release of SME 6.5, which has some more updates and new features and seems already stable with the current RC1. Several Contribs has yet to be adapted for this release, though.
SME 7.0 alpha is based on CentOS 3.x and will certainly soon ported to CentOS 4.0 and offers support for new hardware like S-ATA and Gigbait NICs. But I expect a release not before 10-20 months.
What features are you exactly missing in 6.0(1)?
SME 6.01 offers support for standard SCSI and IDE controllers, even for RAID controllers like ICP. A computer with 1,x GHz and 256 - 512 MB should be IMHO sufficient.
And many, many contribs exist for most tasks. I don't know of any feature my SME 5.6 server had, which I don't have with my SME 6.01.