It's been an enjoyable read Neil, despite going down a couple of blind alleys, and taking the odd scenic route
, you seem to be getting there in the end.
I've been using an i7 system for a couple of years, mainly put together to cope with the huge file sizes of a 1DS MKIII, my system is obviously older than yours, built on an Asus PSP55D Deluxe board, with i7 860 @2.8GHz, 8GB corsair XMS3 DDR3 memory.
Like you I used the built in autotuning facility to overclock to 3526Mhz, which has been stable for the last two years, which runs at around 40C (using 'core temp' to constantly monitor).
The whole setup has run without a glitch, except for once getting a series of BSOD, which was caused by either the CPU fan working lose or the heatsink compound drying out (or perhaps both) causing the CPU to overheat (this was before I installed Core Temp), since I sorted this out with an upgraded fan, it's taken everything thrown at it. My most beneficial upgrade was to install A SSD(Intel 128GB) as a system drive and a CS scratch disk, not so noticeable improvement was increasing memory from 8GB to 16GB.
Probably the weakest link in my set up is the graphics card, Geforce 9500GT, but as I'm not a Gamer, I can live with it's limitations.
I do like the raw power an I7 gives you, I can run what I want in Photoshop without the wait (or pauses) I had previously, I can open any amount of applications, programs, or run multiple tabs on multiple browsers without any strain, and comfortably run a 30inch & 24 inch monitors at the same time.
You only really notice just how good and fast things are on an i7 when you try working on an older machine (like my dual core laptop) where you can go away and make a three course meal while waiting for a PS action to finish.