Recommend the M4, Have not heard if Intel has fixed the 8 mb bug for the 320 yet. They did come out with a firmware about a month ago, But heard that it was not totally effective.
64 Gig is the Min size that I recommend. Win 7 with most of my programs (no games) only takes up around 30 gigs.
Recommend 2 things:
Disable hibernation, Saves 4->6 gigs) and (2) set min / max size for virtual memory to 1024 mb (this save an additional 4 -> 5 Gigs.
For Hibernation: http://support.microsoft.com/kb/920730
For Page File (virual memory): http://windows.microsoft.com/en-US/windows-vista/Change-the-size-of-virtual-memory
USE INTEL sata port, not 3rd party marvel sata port.
Disconnect ALL other HDDs
Set controller to AHCI
After windows installation, reconnect HDDs
If MB controller for sata ports is INTEL, down load and install the latest Intel RST driver Ver 10.6
On sata II vs Sata III SSDs. Biggest performance difference is for the sequencial read / writes. Leat important parameter for a OS + Program drive. Not a BIG performance diff for a "Good" Sata II SSD such as Samsung 470 vs a Sata III drive for access time and for the small file 4K random read / writes which are the IMPORTANT parameters.