Deploy to same model of servers takes 15min or 3 hours

We have 23 Dell Power edge 1950 servers, I installed Windows 7 64bit on server01 and then made a master image. I then deployed the image to all the other servers. Servers 02 - 06 took 15min to deploy the image and servers 07 - 23 took 3 hours or more to deploy. The only difference in the server hardware is the hard-drives.... Servers 01- 06 are SATA whereas Servers 07 - 23 are SAS. I have tried universal deploy, multicast, unicast, including the Dell SAS drivers in the universal deploy image but no luck.

I have also tried to deploy to server 07 which has a SAS drive. I then took a master image of this and tried to image it to another SAS server but it still took over 3 hours.

The SATA drives are 80gb and the SAS drives are 72GB.

Also during business hours I have to do unicast deploys otherwise if I do a multicast deploy noone can access the main servers where Acronis is installed other than the servers im deploying to. So if i want to do a multicast deploy I kick it off out of hours... IP multicasting is enabled on our 3 x Dell switches.