You can change her wrapper, but the kernel still looks the same. Maybe the question to ask is what the difference between a tweaked Vista and Windows 7?
Windows 7 Called Slower than Vista PC World
According to iolo's tests, Windows 7 starts up 42% slower than Vista -- one minute, 34 seconds versus one minute, six seconds -- on a brand new machine when the time trials are run to the point where the machine is usable, at least by iolo's standards.
Does Windows 7 Boost Performance? PCQuest
Win 7 Vs Win Vista
We came across in our test an unexpected fight between the two, while we figured out that the performance of Windows 7 and Windows Vista is actually at par. Windows Vista rather outshone Windows 7 by a couple of percentage points. This is pretty obvious as both Windows 7 and Vista use the same kernel. Microsoft didn't develop a new kernel for Windows 7, rather they have refined the Windows Vista kernel to use in Win 7. However, Windows 7 took less than half the time when compared with Windows vista.
Happy 50th Birthday "Weird Al" Yankovic! Freaking News