Windows 7 found to outperform Vista by about 14% in many tests
Well Windows 7 has finally launched today and the press is full of opinions. A lot of good deals are around if you are looking for a PC.
PC Magazine tested the two operating systems under the same conditions, and they found Windows 7 to be faster than Vista in many significant parameters like startup and browsing using Firefox.
(Note that Windows XP still beats both these in most tests done recently).

