I would agree that the main system partition should be over 200 Gb. You really don't want to have that too tight. I have a 240Gb drive on one laptop. That translates to 212Gb of actual room on the drive. Win7 fully patched, a full suite of Office programs, and just a few Gb (maybe 20? total) of data, and I only have 58 Gb of room left. 

I also was in the camp of multiple partitions to segregate stuff, but I'm leaning away from that. I'd rather use the Windows feature of setting up libraries to organize different types of data. Most normal people can't get their heads around drive partitions, but I think they can be taught about libraries.

The only thing is I still like to keep the system and program files separate from data. Your idea of a fast drive for system and a large drive (slower, but cheap) for data makes a lot of sense to me. I think I am going to do that when I rebuild my main system at home into a Windows 8 machine.