From what I have read to date it seems as if Windows 7 is definately built around the Vista kernel. Let´s face it, it even looks the same. Apparently changes are being made to the background activities (only running when neccesary) making it not so hungry on system resources.
There was even one quote from someone at Microsoft that stated Windows 7 should be able to able to run smoothly on a 1Ghz Processor with 1GB ram, aimed at Netbook use like the Eee PC (Yeah right!!) From tests that I have seen based on the beta, it actually uses 10MB ram more than Vista after a fresh install. (530 MB Vista to 540 MB Win 7).
On the positive side, seeing as it is based on Vista, Windows 7 should (I state should) be stable from day 1. There won´t be as many driver and software related problems and I´m expecting the 64bit architecture to be mainstream by the end of next year. It´s been around long enough now!! I have just changed from 32 to 64 and must say I´m quite pleased with results. This time last year I had tried Ultimate x64 for the first time and it was an absolute nightmare, not so now!!
As for the i7, well there´s even rumours that Intel may bring out another processor with 1160 pins (LGA 1160) for the mainstream next year!! As I said these are rumours and I can only think they will be cheaper to fabricate if they are focused towards the mainstream (whatever that means!!). Personally when I get my i7 (965) setup together I am sticking to it for at least 2-3 years. It has enough power, with the DDR3 memory to take any game/program in it´s stride. I can´t think that anything will come out over the next few years that will want me to change my mind. Unless ofcourse Windows 8 comes out with a 128bit architecture, lol !!!!