What are you using the system for? Are there applications that are compute intensive that you wait around for them to complete? If so, are these applications memory bandwidth limited? The i7 has QPI and integrated memory controllers, memory bandwidth is significantly increased. If this is a gaming system then my guess is that an upgrade is not warranted (frames per second would be your criteria there, and that is more than likely limited by the graphics card).
Here's a side-by-side comparison of the two processors
The X5570 i7 has a max memory bandwidth of 32 GB/sec. The comparison above doesn't tell you what the memory bandwidth for the QX9770 is, but you can find that in various reviews and seems to be in the 5-6 GB/sec range. As you can see, there is a 5x to 6x improvement in memory bandwidth, which would be the major reason for you to upgrade *if* your applications are memory bandwidth limited.
Here's a review of the QX9770 that includes memory bandwidth
Message was edited by: amdn