This is my take, and my personal opinion. I believe Intel, when they made their design changes for Sandybridge they worked out a lot of improvements in code execution. They also made a lot of improvements in power management. Basically this family will come out on the low end first, then the high end later. Be that as it may, to wait for it makes little difference to me, I already bought my X58 board and I7-930.
What I don't think will change is DDR3 memory will still be the standard. As far as computing power, overall, the graphics makes a big difference, so an enthusiast machine will still have the same PCIe bus for their cards. Solid state drives for the OS make a big noticeable difference in the perception of the speed of a computer.
No matter what processor, the computer consists of the sum of all the parts. Toms has shown where bottlenecks can be and for many games, it is not the processor anymore; it's graphics bound. Overclocking my computer, while giving it a higher synthetic score does not make it perceptively faster as I use it. So when it gets down to it, the new chips may be very good; but one can spend a lot of money on a high end system today or a budget system that is ok for most everything but heavy gaming.
I would not speculate on the performance of SB; I will wait to see. Bottom line, I have learned from articles on Toms, how to choose parts for a computer taking the whole system into account.
I do believe Sandybridge will be impressive, in both the low end box and the high end machine. It may well be much faster, but whether it makes a perceptible difference depends on what parts went in and how well it was tuned. Pretty much how it goes today.
Shame is, to go into the X58, thinking that there may be a trickle down on the processors; but I doubt that will happen. As has happened before, when Intel changes processors, they stop making the high end of their previous model. The supply chain dries up, the prices of the high end older chips never drops until they are sold as used parts on Ebay or Craigslist. I can take heart that I can keep my machine current enough by going to SLI with another grahics card and getting a faster SSD.
In the computing world, nothing stands still. Today's king of the hill is yesterday's has been.