glad to see someone started a thread about this issue …because hmm i was just wondering the same thing
…iam running Cubase 5 32bit & Cubase 7 64bit on Windows 8 Pro 64bit & ASIO drivers… Cubase 5 runs really fast, smooth…
so i just installed Cubase 7 64bit & attempted "emphasize ‘attempted’ " …to open/import a Cubase 5 cpr
lol it took a few attempts, about 20 minutes for MixConsole to load the file, at first i couldn’t tell if the app was crashing or what ! …so then i just let it load “approximately 20min” 
CPU is really struggling to run Cubase 7 64bit… my performance meter is peaking up double of what it is in Cubase 5 
… iam going to install a brand new Intel XEON this week sometime, currently iam running an i5 Quad 3.00Hz