I did the Windows 7 RC and the results were so good that I will not buy another Vista machine. Have you read what others are wriiting? It definitely was not slower than Vista but that was not your question.
You wrote "Is there a way to upgrade without effecting performance?" If I were to take your question literally then no. We would have to find ways to slow Windows 7 down to match the old Vista speed.
Hope this helps,
I've read a few things on the internet, but am still confused. Please help! I want to buy a new laptop now (There's a great sale on the system I want and it comes with a free upgrade to Win7). I'm concerned, however, about whether upgrading to Windows 7 will slow down my new system. Would it be much better to wait and get the new laptop after Win7 comes out? Is there a way to upgrade without effecting performance?