[X4U] Snow Leopard: how much room?

[John French]

I'm preparing to move up to Lion by placing Snow Leopard on a 
separate disk partition, from which I will start up when I need to 
run those applications that aren't Lion-ready. Are there any 
authoritative estimates of how large I should make the Snow Leopard 
partition? Are Apple's technical specifications calling for 5 GB of 
free disk space sufficient (enough, plus a little bit) without being 
extravagant?

Thanks,
John French