Hi mate! I have done almost the same thing. I have got Q6600 (bought few months ago, but maybe I was dazed or what...don´t know why I bought this crap..) so last week I bought Q9550. I was prepared to reinstall my w7, but just tried to start my PC first without reinstall....and everything seems to be fine!
Of course, for your better feeling, you can reinstall w7, but if you have some difficulties with it, you don´t need to do it. Just update your windows performance index and watch the system behaviour to be sure...it should be enough mate
Have a good time and greetings from Prague!