16GB? How much of that do you ever use?
As for the Core i5 vs i7, the 7xx series i5s have quad core and good stepping/turbo buckets on them and can actually beat the i7 920 at times (presumably because the i5 gets better turbo while the hyper-threading - which looks like an extra four cores but isn't - has a bit of an overhead in some scenarios). I thought the i7s were slightly overkill and very quickly expensive for what they'd gain me
I had been considering getting a Geforce GTX 260 as well, but decided I could save the money because I don't game much at the moment. I also read that it was "on its way out", so I think there is a new nVidia release in the imminent future.
In the end I'm looking at about £350 for the motherboard, processor and memory. I did find a nice bundle at CCL Online (my dad and his work colleagues use them and have good reports) but by the time I came to check it in the evening then they'd decided it wasn't "out of stock - 2-4 days" but "sorry - no more stock"
It wasn't overclocked, but it was a pre-built and tested bundle for pretty much the same as I was paying for assorted components.