I just wonder if you really need to. I'm also a writer, making pretty heavy duty use of Word, and some non-intensive graphics (just cropping, resizing and so on). My main machine is a Core2 Duo with 2GB of memory (and an almost wholly redundant 7770 graphics card that just came with the system...) I run XP, however, rather than W7. Any time in the past that I've started to experience the slowdown that's especially typical of XP over time (it's less of an issue with W7, admittedly) then I've just reinstalled XP - and it works a treat.
Far be it from me to try to dissuade you from getting a shiny new PC - but is a software rebuild something you've thought about and decided against?
The other thing to think about, of course, is an SSD.
I'm with MechKB, btw: that motherboard/CPU combo is IMHO way over the top for what are - should be - fairly non-demanding applications.