Can someone please clarify this for me.
If I have 3 x 24port 3750G switches connected in a stack. This equals 24ports x 3 = 72 gigabit ports.
If the backplane is 32Gb, does this mean I have 72:32 oversubscription ?
Or am I wrong here with the 3750G switches?
You're right. Presuming all ports on all switches are operating at 1Gbps, you have 1:2.25 oversubscription ratio at the backplane. In most cases, this shouldn't present any issue though. I mean, I've worked with large server farms with oversubscription ratio greater than 1:16 without any perceived problems.
If you want full non-blocking, you can use Cat4948, but you can't stack this platform. Alternatively, you can use Cat6500 for high-density wire-rate GigE. Don't think about Cat4500 though. Its architecture is pretty poor (6Gbs per slot).