From what I've read, the i7 with its new memory architecture is a lot faster GHz to GHz than even the latest Penryn family chipes like my E5450 ones. These days, with applications using so much RAM, memory bandwidth is becomming the major bottleneck in system performance, which the i7 has gone a long way to addressing (so to speak) for the Intel processor family. Note that AMD chip sets had a similar memory architecture to the new i7 chip sets which is why they were better server chips than the Intel Xeon were until the i7.
As for upgrades - whether you should or not depends upon a number of factors.
1. Is your current system more than 3 years old?
2. Does it perform adequately to your needs?
3. If performance lags, will just adding memory (RAM) improve it enough to get another couple of years out of the system?
4. Do you HAVE to have bleading edge hardware?
5. What is the application mix you need to run on your system(s)?
All of these things, and more, should be factored into your decision making process. About 2 years ago I had to decide what to get for a new system. I was starting a new consulting business, wanted to migrate all of my work to Linux, my system was over 3 years old and needed more memory, I wanted to run 64bit software which my old CPU would not do so I could take advantage of >4GB RAM in order to run large databases and multiple virtual machines. So, I looked at what was available, what was just being released, costs, etc. This is what I came up with:
1. Custom built workstation/server w/ 750VA power supply.
2. Intel dual quad-core capable motherboard (S5000XVN).
3. Dual E5450 3GHz Penryn processors (just released and best performing Intel chips for the price at the time).
4. 8GB of fully-buffered ECC RAM (ECC == reliability).
5. Removable 320GB sata boot/system drive with backup carrier and drive.
6. 4x500GB sata system data drives
7. nVidia 8800GT video board w/ dual 24" HD monitors (so I can run a VM or remote system on its own display with the other dedicated to local tasks).
All in all, this has been a great system for my uses. I run 64bit CentOS 5.x, Sun VirtualBox VMM w/ Windows XP and Solaris VMs, Oracle 11i database server, etc. As to why I chose Intel vs. AMD CPU's it's just that I have always been happy with Intel stuff and I wasn't convinced that AMD will be around for the long run, even though they seem to hang in there. Also, I'm a bit prejudiced toward Intel since a number of my best friends have been their CPU designers over the years, like Bruce Ravanel who was one of the original principal architects of the x86-x87 processor family. He and his family have been friends of mine for over 40 years - so I just go with what/who I know...
